Date Calculator
Add or subtract time from a date, or measure the gap between two dates instantly.
Example
Adding 3 months and 10 days to Jan 31, 2026: months first lands on Apr 30 (April has no 31st, so it clamps), then +10 days gives May 10, 2026 (a Sunday). The difference between Jan 1 and Mar 1, 2026 is 59 days (8w 3d, 2 whole months).
How it works
In Add/Subtract mode the tool applies months first (clamping to the last valid day), then adds the equivalent days for weeks and days. In Difference mode it counts whole calendar days between the two dates, then derives weeks (days/7) and an approximate month count from the calendar.
Good to know
This Date Calculator does two distinct jobs in one place. In its Add / Subtract mode you pick a start date, choose whether to add or subtract, and enter any combination of years, months, weeks, and days to land on a future or past calendar date. In Difference mode you enter two dates and it reports the exact gap between them. It is handy for anyone juggling deadlines, contracts, due dates, project milestones, billing cycles, or travel and visa windows who needs a precise calendar answer rather than a rough mental estimate.
The two modes report different things, so read the output accordingly. In Add / Subtract mode the headline is the resulting date, with the day of the week, the total elapsed days from your start date, and the ISO format (YYYY-MM-DD) shown underneath. In Difference mode the headline is the total number of days between your two dates, followed by that same span expressed as weeks plus leftover days, a count of whole calendar months, and a Direction note telling you whether the To date is later or earlier than the From date.
One detail worth understanding is the order of operations and the month-clamping rule. Add / Subtract applies the years and months first, then adds the weeks and days, and if the target month is too short for your day number it snaps to that month's last day. That means the operation is not always reversible: subtracting the same amounts from your result will not always return you to the original date when clamping occurred along the way.
A practical tip: if you only care about a literal day count and want to sidestep all calendar quirks, work entirely in Add / Subtract mode using the Weeks and Days fields and leave Years and Months at zero, since weeks and days are pure 7-day and 1-day arithmetic with no clamping. Note too that everything runs locally in your browser with no time zones or daylight-saving adjustments applied, so each date is treated as a plain calendar day.
Frequently asked questions
What happens when I add a month to January 31?
Months are added by calendar, so January 31 plus one month targets February. Since February has no 31st, the result is clamped to the last day of February (Feb 28, or Feb 29 in a leap year).
How does Difference mode count whole months?
It counts elapsed calendar months between the two dates, subtracting one if the end day-of-month is earlier than the start day-of-month, so a partial final month is not counted. The headline number is always the exact total days.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser. Your inputs never leave your device, and it works offline once loaded.
Is this calculator free?
Yes, completely free with no sign-up and no limits.
People also ask
How many days are between two dates?
Enter the earlier date as the From date and the later one as the To date in Difference mode, and the calculator returns the exact total number of calendar days, along with the equivalent in weeks and days. If you reverse the two dates the day count stays the same and the Direction field flags that the To date is earlier.
Does the date calculator include the start and end day in the count?
In Difference mode it counts the elapsed days between the two dates, which is an exclusive count: the gap from one day to the next day equals one day. If you want both endpoints included, add one to the reported total.
Why does adding one month to the 31st give the 30th or 28th?
Months are added on the calendar, so the result targets the same day number in the next month. When that month has fewer days, the date is clamped to the last valid day, which is why the 31st can become the 30th, or the 28th or 29th in February.
Does this calculator account for leap years?
Yes. It uses your browser's calendar logic, so February 29 in leap years is handled correctly when adding, subtracting, or counting the difference between dates.
Can I calculate a date a certain number of weeks from today?
Yes. The start date defaults to today, so you can leave it as is, enter the number of weeks (and optionally days), and read off the resulting date and its day of the week. Weeks are treated as exactly seven days.
Does the date calculator handle time zones or hours?
No. It works only with whole calendar dates and ignores hours, minutes, and time-zone or daylight-saving shifts. For hour-level or clock-time math you would need a separate time-based tool.
How are whole months counted in the difference between two dates?
It takes the difference in years and months between the two dates and then subtracts one month if the end day-of-month is earlier than the start day-of-month, so a partial final month is not counted. The exact total-days figure remains the primary, most precise result.
Is the result the same if I subtract back the amount I added?
Not always. Because months are applied first and clamped to a month's last day when needed, adding and then subtracting the same values can land on a slightly different date whenever clamping occurred.
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