Free Online Date Tools

Plan date ranges, shifts and availability, inspect timestamps and convert time representations with free online date tools.

Choose the right tool

Use Date Difference for elapsed calendar days, Working Days for weekday counts, and Time Zone Converter for an explicit instant. Weekends, holiday lists, endpoint counting and daylight-saving rules depend on the chosen tool.

Available tools

• Date Difference Calculator

  Count calendar days between two dates; time zones do not affect the result.

• Add / Subtract Days from a Date

  Move a calendar date forward or backward by whole days.

• Age Calculator

  Calculate completed years, months and days at a reference date.

• Time Zone Converter

  Display an explicit-offset date/time in an IANA time zone, including DST.

• ISO Week Number Calculator

  Find the ISO week number, week-year and weekday.

• Working Days Calculator

  Count Monday–Friday days between dates, excluding supplied holidays.

• Date Format Converter

  Convert a strictly specified calendar-date format without guessing day/month order.

• Leap Year Checker

  Check Gregorian leap-year rules and report the number of days in the year.

• Day of Year Calculator

  Calculate the 1-based day number within a Gregorian year.

• Add Business Days

  Add or subtract Monday–Friday working days, skipping optional listed holidays.

• Add Time Duration

  Add or subtract seconds from a 24-hour clock time and report the day offset.

• Monthly Calendar Generator

  Display a Monday-first calendar for the input date’s month.

• Month Start and End Calculator

  Find the first and last calendar date of a month.

• Quarter Date Calculator

  Identify a date’s calendar quarter and its start and end.

• Monday Week Boundaries

  Find Monday and Sunday of the date’s calendar week.

• Day of Week Finder

  Return the English weekday name and ISO weekday number.

• Date Range Generator

  Generate equally spaced calendar dates from a starting date.

• Monthly Recurrence Generator

  Repeat a date monthly, clamping to each month’s last day.

• Nth Weekday of Month

  Find a chosen weekday’s numbered occurrence in a month.

• Last Weekday of Month

  Find the last chosen weekday in a month.

• Weekday Counts in Date Range

  Count how many Mondays through Sundays fall in an inclusive date range.

• Calendar Date List Sorter

  Validate and chronologically sort a list of ISO dates.

• Missing Dates in a List

  List missing calendar days between the earliest and latest supplied dates.

• Duplicate Calendar Date Report

  Validate a date list and report repeated dates and their line numbers.

• Calendar Date List Validator

  Check each date independently and report calendar errors.

• Excel Serial to Date

  Convert an Excel 1900-system whole-day serial to a UTC date.

• Date to Excel Serial

  Convert a date to a whole-day Excel 1900-system serial.

• Julian Day Number Converter

  Convert UTC midnight to an astronomical Julian Date.

• Modified Julian Date Converter

  Calculate Modified Julian Date at UTC midnight.

• Unix Timestamp Day Boundaries

  Get inclusive UTC-day start and exclusive next-day Unix timestamps.

• Calendar Year Progress

  Measure elapsed complete days and remaining days in a calendar year.

• Add Calendar Months

  Add or subtract months while clamping to the target month’s last day.

• Add Calendar Years

  Add or subtract years; February 29 clamps to February 28 when necessary.

• Calendar Date Comparison

  Compare two dates and return their signed calendar-day difference.

• Date Range Overlap Calculator

  Find the inclusive overlap of two calendar date ranges.

• Weeks Between Dates

  Split a signed date difference into complete weeks and remaining days.

• ISO Week Date Formatter

  Format a calendar date as ISO week-year, week and weekday.

• ISO Week Date to Calendar Date

  Convert a strict ISO week date into YYYY-MM-DD.

• UTC HTTP Date Formatter

  Format UTC midnight using the RFC 7231 HTTP-date representation.

• Seconds to Clock Duration

  Format elapsed seconds as days, hours, minutes and seconds.

• Clock Duration to Seconds

  Parse an HH:MM:SS elapsed duration with hours allowed above 23.

• ISO Duration and Seconds Converter

  Convert exact day/hour/minute/second ISO durations to seconds or back.

• Duration List Summary

  Summarize a list of elapsed HH:MM:SS durations with total and average.

• Daily Clock Window Overlap

  Find overlap between two same-day clock windows.

• Timestamp Interval Merger

  Merge overlapping or touching absolute timestamp intervals.

• Free Time Gap Finder

  Find free intervals between busy ranges inside an explicit day window.

• Daily Shift Hours Calculator

  Calculate same-day or overnight elapsed shift time minus an explicit break.

• CSV Timesheet Hours Summary

  Validate daily CSV clock entries and sum paid hours by calendar date.

• Time Billing Increment Rounder

  Round an elapsed duration to a chosen minute increment.

• Multi-Zone Meeting Time Sheet

  Display one explicit meeting instant across an entered timezone list.

• Timezone Offset Transition Finder

  Find timezone UTC-offset changes in a selected calendar year using browser timezone data.

• Next Selected Weekday Finder

  Find the next requested ISO weekday, optionally including the input date.

• Weekend Date List Generator

  List Saturdays and Sundays in an inclusive calendar date range.

• Custom Business Day Checker

  Classify dates using an explicit ISO weekday mask and user-supplied holiday list.

• Fiscal Year and Quarter Calculator

  Map a date to a fiscal year and quarter using a chosen first month.

• 4-4-5 Fiscal Period Builder

  Build a 52-week 4-4-5 retail calendar from an explicit starting date.

• Project Milestone Date Mapper

  Map named calendar-day offsets onto a chosen project start date.

• Timed Agenda Builder

  Assign sequential start/end clock times to labeled minute-duration agenda items.

• Static Work and Break Schedule

  Create a printable work/break plan without a running timer.

• Explicit Deadline Duration Calculator

  Calculate signed time remaining between an explicit reference instant and deadline.

• Signed Unix Timestamp Width Checker

  Report exact whole Unix seconds and signed 32-bit second range compatibility.

• Localized Calendar Date Formatter

  Format one UTC calendar date in a selected locale with full weekday and month names.

• Fixed UTC Offset Clock Converter

  Display an instant using an explicit fixed UTC offset without daylight-saving rules.

• Offset-Aware Timestamp List Sorter

  Sort timestamp strings chronologically, normalizing each result to UTC.

• Timestamp Cadence and Gap Analyzer

  Sort timestamp observations and report consecutive elapsed gaps.

• Equivalent Timestamp Duplicate Finder

  Find timestamp strings that represent the same absolute millisecond.

• UTC Timestamp Bucket Counter

  Count instants into fixed UTC-epoch-aligned minute buckets.

• Consecutive Calendar Date Streaks

  Group unique dates into consecutive-day streaks and report the longest.

• Multiple Date Range Coverage Calculator

  Merge inclusive calendar-date ranges and count distinct covered days.

• UTC Working Hours Between Instants

  Count overlap with explicit Monday–Friday UTC work windows across an interval.

• Repeating Shift Calendar Builder

  Repeat an explicit shift pattern over a chosen date span.

• On-Call Rotation Schedule Builder

  Assign people to equal calendar-day blocks from an explicit start.

• Common Availability Interval Finder

  Intersect multiple participants’ absolute-time availability ranges.

• Date Range Monthly Allocation

  Split an inclusive date range into calendar-month segments with day counts.

• Next Birthday Date Calculator

  Find the next calendar occurrence of a birthday from an explicit reference date.

• Non-Drop Video Timecode Converter

  Convert HH:MM:SS:FF timecodes to frame counts or back at integer frame rates.