Date Calculator
Use this free date calculator to find the difference between two dates or to add and subtract days, weeks, months, or years from a date. The difference mode returns total days, weeks, hours, business days, and a clean years-months-days breakdown. The add and subtract mode returns the resulting date and the day of the week it falls on.
Dates are treated as calendar dates, not timestamps; the calculator does not convert between time zones. Business-day counts exclude weekends but not public holidays, since holidays vary by country and region.
Everything you need for date math
Six features that cover difference and date-shift calculations.
Days, weeks, hours
See the difference in total days, decimal weeks, and total hours all at once.
Years, months, days breakdown
A clean breakdown of the same span as Y/M/D, useful for anniversaries, age, and tenure.
Business days
Counts weekdays (Monday to Friday) only, useful for project deadlines and SLA windows.
Add or subtract any unit
Shift any date by a number of days, weeks, months, or years and see the resulting date.
Weekday of result
See which day of the week the calculated date falls on, instantly.
Mobile-friendly layout
Clean responsive design with native date pickers on phones and desktops.
Who uses a date calculator?
Anyone with a date-driven question.
Project deadlines
Find a deadline date that is N business days from today.
Anniversaries and birthdays
See how many days remain to the next anniversary or how many have passed.
Travel planning
Work out trip duration, calculate return dates, plan multi-week itineraries.
Pregnancy tracking
For a quick gestational-age check, use the dedicated due date calculator for full pregnancy planning.
Loan and contract terms
Calculate maturity dates from a start date plus a number of months or years.
Counting workdays for billing
See the business days in a billing period or between two project milestones.
About date math
A clear guide to calendar arithmetic, business days, and date shifts.
How the calculator measures difference
The browser's Date object stores time as milliseconds since 1 January 1970. The calculator subtracts the start date from the end date in milliseconds, then divides by 86,400,000 (the number of milliseconds in a day) to get total days. Other units follow from there: weeks divide by 7, hours multiply by 24, business days iterate day by day and count only weekdays.
The years-months-days breakdown
Because months and years have different lengths, a single day count can be expressed many ways. The calculator uses the calendar convention of stepping years first, then months, then days. So 25 March 2024 to 25 May 2025 is 1 year, 2 months, 0 days. Most calendar systems, HR systems, and pregnancy trackers use the same approach.
Business days explained
Business days exclude Saturday and Sunday but include all other days. The calculator does not exclude public holidays, because those vary by country and region (Christmas, Eid, Diwali, US federal holidays, UK bank holidays, etc.). For a working-day count tied to a specific country, subtract the relevant public holidays from the calculator's business-day count.
Leap years and the calculator
The calculator inherits the browser Date object's leap-year logic: years divisible by 4 are leap, except centuries unless they are also divisible by 400. So 2024 has 366 days, 2025 has 365, and 2100 will have 365 days. February 29 only appears in leap years, which can shift date math at the day-of-month level when calculating across a non-leap year.
Adding months across month-end
Adding 1 month to 31 January gives 28 February (or 29 in a leap year) because February does not have 31 days. The browser's setMonth method rolls the day forward if needed. This is the safest convention, but it means that adding 1 month to the 31st of a 31-day month sometimes lands on the last day of the next month rather than preserving the day number.
Negative durations
If the end date is before the start date, the calculator shows the difference as a positive number with a negative sign on the years-months-days breakdown. This avoids confusing display while still preserving the direction of the calculation.
Time zones and calendar dates
The calculator treats dates as calendar dates rather than as moments in time. There is no time zone conversion. If you give it 1 January 2025 it interprets that as 1 January 2025 in your browser's local time zone. For most everyday questions (deadlines, anniversaries, age), calendar dates are exactly what you want.
Inclusive versus elapsed counting
Calendar arithmetic has a subtle question: are you counting elapsed days or inclusive days? The calculator counts elapsed days (the gap between two midnights). So Monday to Friday is 4 elapsed days. To count both endpoints (5 days for Monday to Friday), add 1. Choose whichever matches your context.
Why add/subtract mode is separate
The two modes answer fundamentally different questions: difference tells you the gap between two known dates; add/subtract finds a target date from a known starting point and a span. Combining the two in one panel would clutter the screen, so the calculator has a clean toggle at the top.
Frequently asked questions
If you don't find your question here, ask us directly.
It uses the Date object built into the browser to find the number of milliseconds between two dates, then divides by the number of milliseconds in a day, week, or year to give a clean number. For the "add or subtract" mode, it shifts the start date forward or backward by the requested amount and reads the new date back out, including the weekday.
The calculator gives total days, total weeks (decimal), total hours, and a years-months-days breakdown. For example, 1 January 2024 to 1 January 2025 is exactly 366 days (because 2024 is a leap year). The years-months-days view is 1 year 0 months 0 days for that same span.
Business days are days that exclude Saturday and Sunday. The calculator counts every weekday in the date range. It does not exclude public holidays, because those vary by country and region. If you need a working-day count for a specific country, subtract the number of public holidays falling inside the range manually.
Yes. The browser Date object knows leap years (years divisible by 4, except centuries unless they are also divisible by 400). So 2024 has 366 days, 2025 has 365, and 2100 will have 365 even though 2000 had 366. The calculator inherits this from the Date object.
Adding 1 month to 31 January gives 28 February (or 29 in a leap year) because February does not have 31 days. The browser's setMonth method handles this overflow. So if you add a month to the 31st of a 31-day month, you may land on the last day of the next month. Add 12 months instead of 1 year if you want to keep this behaviour predictable.
It is accurate in the everyday sense, but because months and years have different lengths, the same day count can be expressed differently depending on the start date. The calculator uses the convention of stepping years first, then months, then days, which is what most calendar and HR systems do. The total days figure is exact.
You can, but our dedicated age calculator gives a slightly nicer breakdown specifically for ages. For everything else (project deadlines, days until an event, anniversaries, days since a milestone), the date calculator is the right tool.
The calculator works in calendar days, not seconds. Two timestamps on the same calendar day count as 0 days apart even if they are 23 hours and 59 minutes apart. If you need second-level precision (event countdowns, durations of meetings), use our time calculator instead.
Dates are treated as calendar dates, not as timestamps. The calculator does not convert between time zones. If you enter the same calendar date that someone in another time zone gives you, the result will be correct for both of you.
Yes. In add/subtract mode there is a unit selector for days, weeks, months, and years. Weeks add 7 days each. Months and years use the calendar arithmetic described above (so adding 1 year to a leap day rolls to 28 February).
Use add/subtract mode. Enter the start date, choose Add, enter the number of days, weeks, or months, and pick the unit. The result date is displayed with the day of the week. This is useful for project deadlines, loan deadlines, and any "10 working days from today" style question.
Calendar arithmetic has a subtle question: are you counting elapsed days or inclusive days? The calculator counts elapsed days (the difference in midnight-to-midnight calendar dates). To count both endpoints, add 1. For example, "from Monday to Friday" is 4 elapsed days but 5 inclusive days.
Yes. Your dates stay in your browser. Nothing is sent to a server, logged, or shared. You can use the calculator without an account and even offline once the page has loaded.
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