diff --git a/src/day.js b/src/day.js
index 6c3f9ca..2b5d4b6 100644
--- a/src/day.js
+++ b/src/day.js
@@ -1,12 +1,35 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 import {durationDay, durationMinute} from "./duration.js";
 
-var day = interval(
+export const timeDay = timeInterval(
   date => date.setHours(0, 0, 0, 0),
   (date, step) => date.setDate(date.getDate() + step),
   (start, end) => (end - start - (end.getTimezoneOffset() - start.getTimezoneOffset()) * durationMinute) / durationDay,
   date => date.getDate() - 1
 );
 
-export default day;
-export var days = day.range;
+export const timeDays = timeDay.range;
+
+export const utcDay = timeInterval((date) => {
+  date.setUTCHours(0, 0, 0, 0);
+}, (date, step) => {
+  date.setUTCDate(date.getUTCDate() + step);
+}, (start, end) => {
+  return (end - start) / durationDay;
+}, (date) => {
+  return date.getUTCDate() - 1;
+});
+
+export const utcDays = utcDay.range;
+
+export const unixDay = timeInterval((date) => {
+  date.setUTCHours(0, 0, 0, 0);
+}, (date, step) => {
+  date.setUTCDate(date.getUTCDate() + step);
+}, (start, end) => {
+  return (end - start) / durationDay;
+}, (date) => {
+  return Math.floor(date / durationDay);
+});
+
+export const unixDays = unixDay.range;
diff --git a/src/hour.js b/src/hour.js
index 9b944d6..77b77a3 100644
--- a/src/hour.js
+++ b/src/hour.js
@@ -1,15 +1,26 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 import {durationHour, durationMinute, durationSecond} from "./duration.js";
 
-var hour = interval(function(date) {
+export const timeHour = timeInterval((date) => {
   date.setTime(date - date.getMilliseconds() - date.getSeconds() * durationSecond - date.getMinutes() * durationMinute);
-}, function(date, step) {
+}, (date, step) => {
   date.setTime(+date + step * durationHour);
-}, function(start, end) {
+}, (start, end) => {
   return (end - start) / durationHour;
-}, function(date) {
+}, (date) => {
   return date.getHours();
 });
 
-export default hour;
-export var hours = hour.range;
+export const timeHours = timeHour.range;
+
+export const utcHour = timeInterval((date) => {
+  date.setUTCMinutes(0, 0, 0);
+}, (date, step) => {
+  date.setTime(+date + step * durationHour);
+}, (start, end) => {
+  return (end - start) / durationHour;
+}, (date) => {
+  return date.getUTCHours();
+});
+
+export const utcHours = utcHour.range;
diff --git a/src/index.js b/src/index.js
index 9ceb157..d6dfd90 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,86 +1,61 @@
 export {
-  default as timeInterval
+  timeInterval
 } from "./interval.js";
 
 export {
-  default as timeMillisecond,
-  milliseconds as timeMilliseconds,
-  default as utcMillisecond,
-  milliseconds as utcMilliseconds
+  millisecond as utcMillisecond,
+  milliseconds as utcMilliseconds,
+  millisecond as timeMillisecond,
+  milliseconds as timeMilliseconds
 } from "./millisecond.js";
 
 export {
-  default as timeSecond,
-  seconds as timeSeconds,
-  default as utcSecond,
-  seconds as utcSeconds
+  second as utcSecond,
+  seconds as utcSeconds,
+  second as timeSecond,
+  seconds as timeSeconds
 } from "./second.js";
 
 export {
-  default as timeMinute,
-  minutes as timeMinutes
-} from "./minute.js";
-
-export {
-  default as timeHour,
-  hours as timeHours
-} from "./hour.js";
-
-export {
-  default as timeDay,
-  days as timeDays
-} from "./day.js";
-
-export {
-  sunday as timeWeek,
-  sundays as timeWeeks,
-  sunday as timeSunday,
-  sundays as timeSundays,
-  monday as timeMonday,
-  mondays as timeMondays,
-  tuesday as timeTuesday,
-  tuesdays as timeTuesdays,
-  wednesday as timeWednesday,
-  wednesdays as timeWednesdays,
-  thursday as timeThursday,
-  thursdays as timeThursdays,
-  friday as timeFriday,
-  fridays as timeFridays,
-  saturday as timeSaturday,
-  saturdays as timeSaturdays
-} from "./week.js";
-
-export {
-  default as timeMonth,
-  months as timeMonths
-} from "./month.js";
-
-export {
-  default as timeYear,
-  years as timeYears
-} from "./year.js";
-
-export {
-  default as utcMinute,
+  timeMinute,
+  timeMinutes,
+  utcMinute,
   utcMinutes
-} from "./utcMinute.js";
+} from "./minute.js";
 
 export {
-  default as utcHour,
+  timeHour,
+  timeHours,
+  utcHour,
   utcHours
-} from "./utcHour.js";
-
-export {
-  default as utcDay,
-  utcDays
-} from "./utcDay.js";
+} from "./hour.js";
 
 export {
-  default as unixDay,
+  timeDay,
+  timeDays,
+  utcDay,
+  utcDays,
+  unixDay,
   unixDays
-} from "./unixDay.js";
+} from "./day.js";
 
 export {
+  timeSunday as timeWeek,
+  timeSundays as timeWeeks,
+  timeSunday,
+  timeSundays,
+  timeMonday,
+  timeMondays,
+  timeTuesday,
+  timeTuesdays,
+  timeWednesday,
+  timeWednesdays,
+  timeThursday,
+  timeThursdays,
+  timeFriday,
+  timeFridays,
+  timeSaturday,
+  timeSaturdays,
   utcSunday as utcWeek,
   utcSundays as utcWeeks,
   utcSunday,
@@ -97,17 +72,21 @@ export {
   utcFridays,
   utcSaturday,
   utcSaturdays
-} from "./utcWeek.js";
+} from "./week.js";
 
 export {
-  default as utcMonth,
+  timeMonth,
+  timeMonths,
+  utcMonth,
   utcMonths
-} from "./utcMonth.js";
+} from "./month.js";
 
 export {
-  default as utcYear,
+  timeYear,
+  timeYears,
+  utcYear,
   utcYears
-} from "./utcYear.js";
+} from "./year.js";
 
 export {
   utcTicks,
diff --git a/src/interval.js b/src/interval.js
index 2714a81..9c4a37a 100644
--- a/src/interval.js
+++ b/src/interval.js
@@ -1,32 +1,31 @@
-var t0 = new Date,
-    t1 = new Date;
+const t0 = new Date, t1 = new Date;
 
-export default function newInterval(floori, offseti, count, field) {
+export function timeInterval(floori, offseti, count, field) {
 
   function interval(date) {
     return floori(date = arguments.length === 0 ? new Date : new Date(+date)), date;
   }
 
-  interval.floor = function(date) {
+  interval.floor = (date) => {
     return floori(date = new Date(+date)), date;
   };
 
-  interval.ceil = function(date) {
+  interval.ceil = (date) => {
     return floori(date = new Date(date - 1)), offseti(date, 1), floori(date), date;
   };
 
-  interval.round = function(date) {
-    var d0 = interval(date),
-        d1 = interval.ceil(date);
+  interval.round = (date) => {
+    const d0 = interval(date), d1 = interval.ceil(date);
     return date - d0 < d1 - date ? d0 : d1;
   };
 
-  interval.offset = function(date, step) {
+  interval.offset = (date, step) => {
     return offseti(date = new Date(+date), step == null ? 1 : Math.floor(step)), date;
   };
 
-  interval.range = function(start, stop, step) {
-    var range = [], previous;
+  interval.range = (start, stop, step) => {
+    const range = [];
+    let previous;
     start = interval.ceil(start);
     step = step == null ? 1 : Math.floor(step);
     if (!(start < stop) || !(step > 0)) return range; // also handles Invalid Date
@@ -35,10 +34,10 @@ export default function newInterval(floori, offseti, count, field) {
     return range;
   };
 
-  interval.filter = function(test) {
-    return newInterval(function(date) {
+  interval.filter = (test) => {
+    return timeInterval((date) => {
       if (date >= date) while (floori(date), !test(date)) date.setTime(date - 1);
-    }, function(date, step) {
+    }, (date, step) => {
       if (date >= date) {
         if (step < 0) while (++step <= 0) {
           while (offseti(date, -1), !test(date)) {} // eslint-disable-line no-empty
@@ -50,19 +49,19 @@ export default function newInterval(floori, offseti, count, field) {
   };
 
   if (count) {
-    interval.count = function(start, end) {
+    interval.count = (start, end) => {
       t0.setTime(+start), t1.setTime(+end);
       floori(t0), floori(t1);
       return Math.floor(count(t0, t1));
     };
 
-    interval.every = function(step) {
+    interval.every = (step) => {
       step = Math.floor(step);
       return !isFinite(step) || !(step > 0) ? null
           : !(step > 1) ? interval
           : interval.filter(field
-              ? function(d) { return field(d) % step === 0; }
-              : function(d) { return interval.count(0, d) % step === 0; });
+              ? (d) => field(d) % step === 0
+              : (d) => interval.count(0, d) % step === 0);
     };
   }
 
diff --git a/src/millisecond.js b/src/millisecond.js
index d89585c..e3aa380 100644
--- a/src/millisecond.js
+++ b/src/millisecond.js
@@ -1,26 +1,25 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 
-var millisecond = interval(function() {
+export const millisecond = timeInterval(() => {
   // noop
-}, function(date, step) {
+}, (date, step) => {
   date.setTime(+date + step);
-}, function(start, end) {
+}, (start, end) => {
   return end - start;
 });
 
 // An optimized implementation for this simple case.
-millisecond.every = function(k) {
+millisecond.every = (k) => {
   k = Math.floor(k);
   if (!isFinite(k) || !(k > 0)) return null;
   if (!(k > 1)) return millisecond;
-  return interval(function(date) {
+  return timeInterval((date) => {
     date.setTime(Math.floor(date / k) * k);
-  }, function(date, step) {
+  }, (date, step) => {
     date.setTime(+date + step * k);
-  }, function(start, end) {
+  }, (start, end) => {
     return (end - start) / k;
   });
 };
 
-export default millisecond;
-export var milliseconds = millisecond.range;
+export const milliseconds = millisecond.range;
diff --git a/src/minute.js b/src/minute.js
index 2ed894b..ba8e4d9 100644
--- a/src/minute.js
+++ b/src/minute.js
@@ -1,15 +1,26 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 import {durationMinute, durationSecond} from "./duration.js";
 
-var minute = interval(function(date) {
+export const timeMinute = timeInterval((date) => {
   date.setTime(date - date.getMilliseconds() - date.getSeconds() * durationSecond);
-}, function(date, step) {
+}, (date, step) => {
   date.setTime(+date + step * durationMinute);
-}, function(start, end) {
+}, (start, end) => {
   return (end - start) / durationMinute;
-}, function(date) {
+}, (date) => {
   return date.getMinutes();
 });
 
-export default minute;
-export var minutes = minute.range;
+export const timeMinutes = timeMinute.range;
+
+export const utcMinute = timeInterval((date) => {
+  date.setUTCSeconds(0, 0);
+}, (date, step) => {
+  date.setTime(+date + step * durationMinute);
+}, (start, end) => {
+  return (end - start) / durationMinute;
+}, (date) => {
+  return date.getUTCMinutes();
+});
+
+export const utcMinutes = utcMinute.range;
diff --git a/src/month.js b/src/month.js
index ac995de..6dab69c 100644
--- a/src/month.js
+++ b/src/month.js
@@ -1,15 +1,27 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 
-var month = interval(function(date) {
+export const timeMonth = timeInterval((date) => {
   date.setDate(1);
   date.setHours(0, 0, 0, 0);
-}, function(date, step) {
+}, (date, step) => {
   date.setMonth(date.getMonth() + step);
-}, function(start, end) {
+}, (start, end) => {
   return end.getMonth() - start.getMonth() + (end.getFullYear() - start.getFullYear()) * 12;
-}, function(date) {
+}, (date) => {
   return date.getMonth();
 });
 
-export default month;
-export var months = month.range;
+export const timeMonths = timeMonth.range;
+
+export const utcMonth = timeInterval((date) => {
+  date.setUTCDate(1);
+  date.setUTCHours(0, 0, 0, 0);
+}, (date, step) => {
+  date.setUTCMonth(date.getUTCMonth() + step);
+}, (start, end) => {
+  return end.getUTCMonth() - start.getUTCMonth() + (end.getUTCFullYear() - start.getUTCFullYear()) * 12;
+}, (date) => {
+  return date.getUTCMonth();
+});
+
+export const utcMonths = utcMonth.range;
diff --git a/src/second.js b/src/second.js
index 62069ef..47b2f43 100644
--- a/src/second.js
+++ b/src/second.js
@@ -1,15 +1,14 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 import {durationSecond} from "./duration.js";
 
-var second = interval(function(date) {
+export const second = timeInterval((date) => {
   date.setTime(date - date.getMilliseconds());
-}, function(date, step) {
+}, (date, step) => {
   date.setTime(+date + step * durationSecond);
-}, function(start, end) {
+}, (start, end) => {
   return (end - start) / durationSecond;
-}, function(date) {
+}, (date) => {
   return date.getUTCSeconds();
 });
 
-export default second;
-export var seconds = second.range;
+export const seconds = second.range;
diff --git a/src/ticks.js b/src/ticks.js
index ff71c76..c314789 100644
--- a/src/ticks.js
+++ b/src/ticks.js
@@ -1,19 +1,13 @@
 import {bisector, tickStep} from "d3-array";
 import {durationDay, durationHour, durationMinute, durationMonth, durationSecond, durationWeek, durationYear} from "./duration.js";
-import millisecond from "./millisecond.js";
-import second from "./second.js";
-import minute from "./minute.js";
-import hour from "./hour.js";
-import day from "./day.js";
-import {sunday as week} from "./week.js";
-import month from "./month.js";
-import year from "./year.js";
-import utcMinute from "./utcMinute.js";
-import utcHour from "./utcHour.js";
-import unixDay from "./unixDay.js";
-import {utcSunday as utcWeek} from "./utcWeek.js";
-import utcMonth from "./utcMonth.js";
-import utcYear from "./utcYear.js";
+import {millisecond} from "./millisecond.js";
+import {second} from "./second.js";
+import {timeMinute, utcMinute} from "./minute.js";
+import {timeHour, utcHour} from "./hour.js";
+import {timeDay, unixDay} from "./day.js";
+import {timeSunday, utcSunday} from "./week.js";
+import {timeMonth, utcMonth} from "./month.js";
+import {timeYear, utcYear} from "./year.js";
 
 function ticker(year, month, week, day, hour, minute) {
 
@@ -58,7 +52,7 @@ function ticker(year, month, week, day, hour, minute) {
   return [ticks, tickInterval];
 }
 
-const [utcTicks, utcTickInterval] = ticker(utcYear, utcMonth, utcWeek, unixDay, utcHour, utcMinute);
-const [timeTicks, timeTickInterval] = ticker(year, month, week, day, hour, minute);
+const [utcTicks, utcTickInterval] = ticker(utcYear, utcMonth, utcSunday, unixDay, utcHour, utcMinute);
+const [timeTicks, timeTickInterval] = ticker(timeYear, timeMonth, timeSunday, timeDay, timeHour, timeMinute);
 
 export {utcTicks, utcTickInterval, timeTicks, timeTickInterval};
diff --git a/src/unixDay.js b/src/unixDay.js
deleted file mode 100644
index bbb1bea..0000000
--- a/src/unixDay.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import interval from "./interval.js";
-import {durationDay} from "./duration.js";
-
-var unixDay = interval(function(date) {
-  date.setUTCHours(0, 0, 0, 0);
-}, function(date, step) {
-  date.setUTCDate(date.getUTCDate() + step);
-}, function(start, end) {
-  return (end - start) / durationDay;
-}, function(date) {
-  return Math.floor(date / durationDay);
-});
-
-export default unixDay;
-export var unixDays = unixDay.range;
diff --git a/src/utcDay.js b/src/utcDay.js
deleted file mode 100644
index 8023be1..0000000
--- a/src/utcDay.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import interval from "./interval.js";
-import {durationDay} from "./duration.js";
-
-var utcDay = interval(function(date) {
-  date.setUTCHours(0, 0, 0, 0);
-}, function(date, step) {
-  date.setUTCDate(date.getUTCDate() + step);
-}, function(start, end) {
-  return (end - start) / durationDay;
-}, function(date) {
-  return date.getUTCDate() - 1;
-});
-
-export default utcDay;
-export var utcDays = utcDay.range;
diff --git a/src/utcHour.js b/src/utcHour.js
deleted file mode 100644
index 98b8822..0000000
--- a/src/utcHour.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import interval from "./interval.js";
-import {durationHour} from "./duration.js";
-
-var utcHour = interval(function(date) {
-  date.setUTCMinutes(0, 0, 0);
-}, function(date, step) {
-  date.setTime(+date + step * durationHour);
-}, function(start, end) {
-  return (end - start) / durationHour;
-}, function(date) {
-  return date.getUTCHours();
-});
-
-export default utcHour;
-export var utcHours = utcHour.range;
diff --git a/src/utcMinute.js b/src/utcMinute.js
deleted file mode 100644
index 4e5e7e5..0000000
--- a/src/utcMinute.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import interval from "./interval.js";
-import {durationMinute} from "./duration.js";
-
-var utcMinute = interval(function(date) {
-  date.setUTCSeconds(0, 0);
-}, function(date, step) {
-  date.setTime(+date + step * durationMinute);
-}, function(start, end) {
-  return (end - start) / durationMinute;
-}, function(date) {
-  return date.getUTCMinutes();
-});
-
-export default utcMinute;
-export var utcMinutes = utcMinute.range;
diff --git a/src/utcMonth.js b/src/utcMonth.js
deleted file mode 100644
index 3991b18..0000000
--- a/src/utcMonth.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import interval from "./interval.js";
-
-var utcMonth = interval(function(date) {
-  date.setUTCDate(1);
-  date.setUTCHours(0, 0, 0, 0);
-}, function(date, step) {
-  date.setUTCMonth(date.getUTCMonth() + step);
-}, function(start, end) {
-  return end.getUTCMonth() - start.getUTCMonth() + (end.getUTCFullYear() - start.getUTCFullYear()) * 12;
-}, function(date) {
-  return date.getUTCMonth();
-});
-
-export default utcMonth;
-export var utcMonths = utcMonth.range;
diff --git a/src/utcWeek.js b/src/utcWeek.js
deleted file mode 100644
index e36fac8..0000000
--- a/src/utcWeek.js
+++ /dev/null
@@ -1,29 +0,0 @@
-import interval from "./interval.js";
-import {durationWeek} from "./duration.js";
-
-function utcWeekday(i) {
-  return interval(function(date) {
-    date.setUTCDate(date.getUTCDate() - (date.getUTCDay() + 7 - i) % 7);
-    date.setUTCHours(0, 0, 0, 0);
-  }, function(date, step) {
-    date.setUTCDate(date.getUTCDate() + step * 7);
-  }, function(start, end) {
-    return (end - start) / durationWeek;
-  });
-}
-
-export var utcSunday = utcWeekday(0);
-export var utcMonday = utcWeekday(1);
-export var utcTuesday = utcWeekday(2);
-export var utcWednesday = utcWeekday(3);
-export var utcThursday = utcWeekday(4);
-export var utcFriday = utcWeekday(5);
-export var utcSaturday = utcWeekday(6);
-
-export var utcSundays = utcSunday.range;
-export var utcMondays = utcMonday.range;
-export var utcTuesdays = utcTuesday.range;
-export var utcWednesdays = utcWednesday.range;
-export var utcThursdays = utcThursday.range;
-export var utcFridays = utcFriday.range;
-export var utcSaturdays = utcSaturday.range;
diff --git a/src/utcYear.js b/src/utcYear.js
deleted file mode 100644
index ee89764..0000000
--- a/src/utcYear.js
+++ /dev/null
@@ -1,26 +0,0 @@
-import interval from "./interval.js";
-
-var utcYear = interval(function(date) {
-  date.setUTCMonth(0, 1);
-  date.setUTCHours(0, 0, 0, 0);
-}, function(date, step) {
-  date.setUTCFullYear(date.getUTCFullYear() + step);
-}, function(start, end) {
-  return end.getUTCFullYear() - start.getUTCFullYear();
-}, function(date) {
-  return date.getUTCFullYear();
-});
-
-// An optimized implementation for this simple case.
-utcYear.every = function(k) {
-  return !isFinite(k = Math.floor(k)) || !(k > 0) ? null : interval(function(date) {
-    date.setUTCFullYear(Math.floor(date.getUTCFullYear() / k) * k);
-    date.setUTCMonth(0, 1);
-    date.setUTCHours(0, 0, 0, 0);
-  }, function(date, step) {
-    date.setUTCFullYear(date.getUTCFullYear() + step * k);
-  });
-};
-
-export default utcYear;
-export var utcYears = utcYear.range;
diff --git a/src/week.js b/src/week.js
index c0f1b03..f75ff52 100644
--- a/src/week.js
+++ b/src/week.js
@@ -1,29 +1,56 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 import {durationMinute, durationWeek} from "./duration.js";
 
-function weekday(i) {
-  return interval(function(date) {
+function timeWeekday(i) {
+  return timeInterval((date) => {
     date.setDate(date.getDate() - (date.getDay() + 7 - i) % 7);
     date.setHours(0, 0, 0, 0);
-  }, function(date, step) {
+  }, (date, step) => {
     date.setDate(date.getDate() + step * 7);
-  }, function(start, end) {
+  }, (start, end) => {
     return (end - start - (end.getTimezoneOffset() - start.getTimezoneOffset()) * durationMinute) / durationWeek;
   });
 }
 
-export var sunday = weekday(0);
-export var monday = weekday(1);
-export var tuesday = weekday(2);
-export var wednesday = weekday(3);
-export var thursday = weekday(4);
-export var friday = weekday(5);
-export var saturday = weekday(6);
+export const timeSunday = timeWeekday(0);
+export const timeMonday = timeWeekday(1);
+export const timeTuesday = timeWeekday(2);
+export const timeWednesday = timeWeekday(3);
+export const timeThursday = timeWeekday(4);
+export const timeFriday = timeWeekday(5);
+export const timeSaturday = timeWeekday(6);
 
-export var sundays = sunday.range;
-export var mondays = monday.range;
-export var tuesdays = tuesday.range;
-export var wednesdays = wednesday.range;
-export var thursdays = thursday.range;
-export var fridays = friday.range;
-export var saturdays = saturday.range;
+export const timeSundays = timeSunday.range;
+export const timeMondays = timeMonday.range;
+export const timeTuesdays = timeTuesday.range;
+export const timeWednesdays = timeWednesday.range;
+export const timeThursdays = timeThursday.range;
+export const timeFridays = timeFriday.range;
+export const timeSaturdays = timeSaturday.range;
+
+function utcWeekday(i) {
+  return timeInterval((date) => {
+    date.setUTCDate(date.getUTCDate() - (date.getUTCDay() + 7 - i) % 7);
+    date.setUTCHours(0, 0, 0, 0);
+  }, (date, step) => {
+    date.setUTCDate(date.getUTCDate() + step * 7);
+  }, (start, end) => {
+    return (end - start) / durationWeek;
+  });
+}
+
+export const utcSunday = utcWeekday(0);
+export const utcMonday = utcWeekday(1);
+export const utcTuesday = utcWeekday(2);
+export const utcWednesday = utcWeekday(3);
+export const utcThursday = utcWeekday(4);
+export const utcFriday = utcWeekday(5);
+export const utcSaturday = utcWeekday(6);
+
+export const utcSundays = utcSunday.range;
+export const utcMondays = utcMonday.range;
+export const utcTuesdays = utcTuesday.range;
+export const utcWednesdays = utcWednesday.range;
+export const utcThursdays = utcThursday.range;
+export const utcFridays = utcFriday.range;
+export const utcSaturdays = utcSaturday.range;
diff --git a/src/year.js b/src/year.js
index a86872d..9eadff3 100644
--- a/src/year.js
+++ b/src/year.js
@@ -1,26 +1,49 @@
-import interval from "./interval.js";
+import {timeInterval} from "./interval.js";
 
-var year = interval(function(date) {
+export const timeYear = timeInterval((date) => {
   date.setMonth(0, 1);
   date.setHours(0, 0, 0, 0);
-}, function(date, step) {
+}, (date, step) => {
   date.setFullYear(date.getFullYear() + step);
-}, function(start, end) {
+}, (start, end) => {
   return end.getFullYear() - start.getFullYear();
-}, function(date) {
+}, (date) => {
   return date.getFullYear();
 });
 
 // An optimized implementation for this simple case.
-year.every = function(k) {
-  return !isFinite(k = Math.floor(k)) || !(k > 0) ? null : interval(function(date) {
+timeYear.every = (k) => {
+  return !isFinite(k = Math.floor(k)) || !(k > 0) ? null : timeInterval((date) => {
     date.setFullYear(Math.floor(date.getFullYear() / k) * k);
     date.setMonth(0, 1);
     date.setHours(0, 0, 0, 0);
-  }, function(date, step) {
+  }, (date, step) => {
     date.setFullYear(date.getFullYear() + step * k);
   });
 };
 
-export default year;
-export var years = year.range;
+export const timeYears = timeYear.range;
+
+export const utcYear = timeInterval((date) => {
+  date.setUTCMonth(0, 1);
+  date.setUTCHours(0, 0, 0, 0);
+}, (date, step) => {
+  date.setUTCFullYear(date.getUTCFullYear() + step);
+}, (start, end) => {
+  return end.getUTCFullYear() - start.getUTCFullYear();
+}, (date) => {
+  return date.getUTCFullYear();
+});
+
+// An optimized implementation for this simple case.
+utcYear.every = (k) => {
+  return !isFinite(k = Math.floor(k)) || !(k > 0) ? null : timeInterval((date) => {
+    date.setUTCFullYear(Math.floor(date.getUTCFullYear() / k) * k);
+    date.setUTCMonth(0, 1);
+    date.setUTCHours(0, 0, 0, 0);
+  }, (date, step) => {
+    date.setUTCFullYear(date.getUTCFullYear() + step * k);
+  });
+};
+
+export const utcYears = utcYear.range;