About DateSpan
What DateSpan calculates
DateSpan is a free, browser-based suite of six date and time tools. Every calculation runs entirely in your browser — no accounts, no tracking, no data sent anywhere.
Days, hours, minutes, or seconds between two dates
Project timelines with Gantt-style activity planning
Weekly hours, gross pay, tax, and net pay estimates
Business days excluding weekends and public holidays
Public holidays for 10 countries across any year
Date and time conversions across 50+ time zones
Example uses
- →How many days until my contract ends on Dec 31?
- →How many workdays are left in Q3, excluding federal holidays?
- →I worked 42 hours this week at $55/hr — what is my estimated take-home pay?
- →When does a 90-day project finish if it starts June 1, counting only weekdays?
- →What time is 3 PM New York in Tokyo and London?
- →Which US federal holidays fall in November this year?
Who uses DateSpan
Have a question about how a specific calculation works? See the FAQ below.
The tools
What DateSpan includes
How it works
Calculations, explained
Date duration
The calculator subtracts the start date from the end date using calendar arithmetic. The result is the number of elapsed days (not including the end date). Hours, minutes, and seconds are derived by multiplying days by the appropriate factor. Workdays-only mode iterates over each day and skips Saturdays and Sundays. Holiday exclusion removes any US federal holiday that falls within the range.
Project Planner
Each activity row stores a name, start date, and end date. Days are calculated using the same calendar arithmetic as the Date Duration Calculator, with a toggle to count all days, workdays only (Mon–Fri), or weekends only. The Gantt chart renders each activity as a proportional bar across a shared timeline — activities with no dates are hidden from the chart. The summary bar reflects the earliest start and latest end across all activities.
Time Sheet
Hours are entered per task per day and summed across rows and columns in real time. Gross pay is calculated as total hours multiplied by the hourly rate. Estimated tax is the gross pay multiplied by the user-supplied tax rate percentage. Estimated net pay is gross minus estimated tax. These are estimates only — the calculator does not account for tax brackets, Social Security, Medicare, benefits, or other individual paycheck factors.
Business days
Business days are defined as Monday through Friday. The calculator walks the date range day by day, counting only weekdays. Federal holidays are identified by their IANA-standard rules (e.g. "last Monday of May" for Memorial Day) and subtracted from the count when the exclusion toggle is on. Custom excluded dates are also subtracted; custom included dates are added back even if they would otherwise be excluded.
Holiday calendar
Holidays are generated on-the-fly for any requested year using algorithmic rules — not a static database. Easter is computed using the Anonymous Gregorian algorithm. Floating holidays (e.g. "second Monday of October") use modular weekday arithmetic. Observed substitutions (when a holiday falls on a weekend) shift the observed date to the nearest weekday.
Time zone conversion
The converter uses the browser's built-in Intl.DateTimeFormat API to determine the UTC offset for each time zone at the selected moment. This means DST transitions are handled automatically — the offset shown for a summer date in New York will be UTC−4, while a winter date will show UTC−5. The reference time is parsed as local time in the source zone, converted to UTC, then re-expressed in each target zone.
Accuracy notes
What we get right — and where to be careful
DateSpan aims for high accuracy, but no tool covers every edge case. Here's an honest breakdown.
Holiday dates are calculated algorithmically — floating dates, observed substitutions, and Easter-based holidays are all derived from rules, not static lists.
Time zone offsets use the browser's Intl API, which is DST-aware and reflects the correct UTC offset for any given moment.
Business day counting is calendar-based and unaffected by DST transitions.
Regional or state-level holidays (e.g. Good Friday in some US states, provincial holidays in Canada) are not included — only nationally recognised public holidays.
India's holiday dates for Holi, Dussehra, and Diwali are approximate — these are lunar-calendar holidays that shift each year and are listed as common observed dates.
FAQ
Frequently asked questions
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