Date & duration
To move a date forward or back, pick the start date, choose add or subtract, and enter the number of years, months, weeks, or days. You get the exact resulting date with its weekday and ISO week. Switch to business-day mode to skip weekends and a country's public holidays.
0 days after Tuesday, August 4, 2026 is
2026-08-04
Tuesday, August 4, 2026
A date calculator answers the everyday question "what date is it going to be?" You know a starting point and an offset, and you need the precise calendar date that lands on. The classic cases are a deadline ("net 30 from the invoice date"), a milestone ("90 days after surgery", "a year and a day after the closing"), a renewal ("the subscription bills six months from sign-up"), or simple planning ("three weeks before the wedding"). Doing this in your head is error-prone because months have different lengths, leap years add a day, and the answer often has to skip weekends. This tool removes the guesswork: enter the start date and the offset, and it returns the resulting date together with the day of the week and the ISO week number, so you can drop it straight into a contract, a calendar, or a project plan.
There are two completely different ways to count forward, and choosing the wrong one is the most common mistake people make with dates. Calendar mode counts every single day. It is the right choice when the rule is expressed in real time, such as "within one year" or "30 calendar days", and it lets you combine years, months, weeks, and days in a single calculation. Business-day mode counts only working days. It steps over Saturdays and Sundays, and if you pick a country it also steps over that country's public holidays, which it loads automatically. Use it whenever the rule says "business days" or "working days", which is typical of payment terms, shipping estimates, notice periods, and many legal filing windows. The two methods can produce dates weeks apart over a long span, so always match the mode to the wording of the rule you are applying.
Adding months is surprisingly subtle. What is one month after 31 January? There is no 31 February, so the tool clamps the day to the last valid day of the target month, giving 28 February in a common year and 29 February in a leap year. This clamping behaviour is the same one spreadsheets and the ISO 8601 standard use, and it is why a monthly plan that starts on the 31st renews on the 30th, 28th, or 29th in the shorter months and snaps back to the 31st whenever the month is long enough. Years are applied as a block of twelve months, so the same day-clamping protects 29 February: one year after 29 February 2024 resolves to 28 February 2025. Once the year and month shift is settled, the calculator adds any whole weeks and days as exact 24-hour offsets. Because every date is anchored to UTC midnight, those offsets never drift by an hour across a daylight saving transition, which is a real bug in naive local-time date math.
Most date-math questions fall into a handful of patterns. Here is how each one maps onto the calculator above, so you can reproduce the answer for your own dates.
Every calculation is encoded in the page URL, so the Share button copies a link that reopens the tool with your exact start date, direction, offset, and mode already filled in. That is handy for sending a deadline to a colleague or saving a renewal date for later. You can also embed the calculator on your own site with the Embed button, which generates a lightweight iframe snippet that respects your visitor's light or dark theme.
If you already know both ends and want the gap between them, use the days-between tool instead. For a pure working-day count between two dates that also subtracts public holidays, use the working-days calculator, and to work out an exact age or anniversary from a birth date, try the age calculator.
Pick your start date, choose add or subtract, and type how many years, months, weeks, or days you want to move. The calculator returns the exact resulting date along with its day of the week and ISO week number. For example, 90 days after 1 January 2026 is 1 April 2026, which falls on a Wednesday.
Calendar mode counts every day, including weekends and holidays, and lets you combine years, months, weeks, and days in one go. Business-day mode counts only working days, skipping Saturdays and Sundays, and optionally the public holidays of a country you select. Use business-day mode for things like payment terms, court or filing deadlines, and project timelines.
Month math clamps to the end of the target month. Adding one month to 31 January gives 28 February (or 29 February in a leap year) rather than spilling into March. This matches how spreadsheets and the ISO 8601 duration model behave, so a monthly subscription that starts on the 31st renews on the last day of each shorter month.
A week is always seven days and a day is always 24 hours, so those offsets are fixed. Months and years vary in length: a month can be 28 to 31 days and a year can be 365 or 366 days. The tool applies the year and month change first, clamps the day if needed, then adds the exact week and day offset, which is the order that produces the answer people expect.
No. All date arithmetic is anchored to UTC midnight, so adding or subtracting whole days never drifts by an hour around a daylight saving change. The output is a calendar date, not a wall-clock time, so it is the same whether you are in New York, London, or Tokyo.