Date Calculator
Count days between two dates, or add and subtract time from any date — no mental calendar gymnastics.
This date calculator does two jobs. First, it counts the exact number of days between any two dates — including weeks-and-days breakdowns. Second, it adds or subtracts a period (days, weeks, months) from a start date and tells you the resulting date. Both results appear the moment your inputs are complete.
Typical uses: how many days until a deadline or holiday, what date is 90 days from today for a contract or returns window, how long a project actually ran, or which date falls 6 weeks after an appointment. Doing this by hand across month boundaries and leap years invites off-by-one mistakes; the calculator follows the real calendar.
Like every ConvertForever tool, it runs fully in your browser — instant, free, and nothing is sent to a server.
How to use the date calculator
- Pick a mode: difference between two dates, or add/subtract from a date.
- For a difference, enter the start and end dates and read the day count instantly.
- To add or subtract, enter the start date, then the number of days, weeks or months.
- Read the resulting date, including the day of the week.
- Adjust any input and the result recalculates live.
Inclusive or exclusive counting?
"How many days between 1 May and 3 May?" can honestly be answered 2 or 3, depending on whether you count both endpoints. This calculator counts the gap between the dates (exclusive of the start day), which is the convention used for durations, deadlines, and date arithmetic. If your context counts both endpoints — some rental and dosing schedules do — add one to the result.
Adding months has its own subtlety: one month after 31 January cannot be 31 February, so the calculator clamps to the last valid day of the target month (28 or 29 February), matching how spreadsheets and most legal conventions behave.
The two modes and what each returns
Difference mode takes two dates and reports the span between them, both as a total number of days and as a tidier weeks-and-days breakdown. It is the mode for "how long until" and "how long since" questions, from a countdown to a holiday to the exact length a project ran.
Add-or-subtract mode takes one date plus a period — so many days, weeks, or months — and returns the resulting calendar date along with its day of the week. Use it to project forward to a deadline or backward to a start date, without flipping through a calendar and counting squares.
A worked example
A shop offers a 30-day return window on a purchase made on 20 January 2026. Put 20 January into add-or-subtract mode, add 30 days, and it returns 19 February 2026 — a Thursday — as the last day to return the item. No need to work out that January has 31 days and juggle the rollover into February by hand.
Switch to difference mode to check the other direction: from 20 January to 19 February is 30 days, confirming the window. The two modes are inverses of each other, which makes it easy to verify a date you have calculated one way by recomputing it the other.
How leap years and month boundaries are handled
The calculator follows the real Gregorian calendar rather than assuming uniform month lengths, so leap years contribute their extra day automatically: any span crossing 29 February picks up that day, and 2024, 2028 and other leap years count 366 days. You never have to remember which years qualify.
Adding whole months respects each month's true length. One month after 31 March lands on 30 April, because April has no 31st, and the tool clamps to the last valid day rather than silently spilling into May. This matches how spreadsheets and most contracts treat month-based periods.
Calendar days versus business days
This tool works in calendar days, so weekends and public holidays are included in every count. For a straight duration — a holiday countdown, a subscription period, the age of a document — that is exactly what you want.
For working-day questions such as delivery estimates or legal notice periods, calendar counting will overstate the working time. A rough conversion is to treat five business days as about seven calendar days, but for anything binding you will need to subtract the specific weekends and holidays that fall inside the span.
Everyday uses
The common cases are deadlines and windows: what date is 90 days from signing, when a 14-day cooling-off period ends, how many days remain until an exam, or how long ago an invoice was issued. Each is a single entry once you pick the right mode.
It is equally handy for planning and record-keeping — counting the days a project actually took, finding the date six weeks after an appointment, or checking whether two events are further apart than they feel. Because you set both inputs, today never has to be involved unless you want it to be.
Accuracy, time zones and privacy
The calculator counts whole calendar days and does not deal in hours, so it ignores time-of-day and daylight-saving shifts entirely — a date is a date regardless of the clock. That keeps results predictable and free of the off-by-one surprises that time-zone maths can introduce.
Everything is computed in your browser using its own calendar logic, so results are instant and nothing you enter is sent to a server. There is no sign-up and no limit on how many dates you compare.
Frequently asked questions
Is the date calculator free to use?
Yes — free, unlimited, and available on any device with a browser. No sign-up required.
Does it count the start and end date?
It counts the days between the two dates, so the start day itself is not included. Add 1 if your situation counts both endpoints.
Can I add business days instead of calendar days?
The calculator works in calendar days, weeks, and months. For working-day arithmetic, count weekends manually or add roughly 7 calendar days for every 5 business days as an approximation.
How are leap years handled?
Automatically. The tool uses real calendar rules, so 2024, 2028 and other leap years contribute 366 days and 29 February is handled correctly.
What happens when I add a month to the 31st?
If the target month is shorter, the result clamps to its last day. One month after 31 January is 28 February (29 in a leap year).
Can I calculate a date 90 days from today?
Yes — that is exactly what the add/subtract mode is for. Enter today as the start date, add 90 days, and you get the precise calendar date and weekday.