Date Calculator
Calculate days between two dates, add or subtract days from a date, and find the day of the week.
How many days until the deadline? What date is 90 days from today? How long has it been since a milestone? Counting days by hand across month boundaries and leap years is fiddly and error-prone, and this calculator removes the guesswork — find the exact number of days between two dates, or add and subtract days from any starting date to land on a precise result.
It is useful far beyond idle curiosity: tracking project deadlines and contract terms, counting down to a wedding or vacation, working out a baby's age in days, calculating notice periods, or figuring out when a 30-day return window closes. Because it accounts for the uneven lengths of months and for leap years automatically, you get a reliable answer in seconds instead of flipping through a calendar and hoping you didn't skip a row.
Plug in some numbers —
we'll crunch.
How to use
- 1Select 'Days between two dates' to find the difference.
- 2Or select 'Add/subtract days' to find a date in the future or past.
- 3Enter the required dates.
- 4See the result with weekday information.
How it works
To find the span between two dates, the tool converts each date to a running day count (essentially the number of days since a fixed reference point) and subtracts. This neatly sidesteps the messy bookkeeping of different month lengths — 28, 30, or 31 days — and of February's leap-year exception, because all of that is already baked into the day count.
Adding or subtracting days works the same way in reverse: it converts the start date to a day count, adds or removes the given number of days, then converts back to a calendar date. The one decision that affects the answer is whether you count inclusively (counting both the start and end day) or exclusively (the gap between them), which can differ by one — a distinction that matters for things like rental periods and notice deadlines.
Worked examples
Counting down to a deadline
Today is June 10, 2026, and a project is due September 1, 2026.
- Days left in June: 20. All of July: 31. All of August: 31.
- Plus the first day of September: but typically count up to the due date.
- Total ≈ 83 days.
About 83 days remain — roughly 12 weeks. Seeing it as a day count (not just 'a couple of months') makes planning the workload far more concrete.
Finding a future date
A product has a 45-day return window starting May 20, 2026.
- 11 days left in May gets you to May 31.
- Remaining 34 days fall in June and into July.
- Day 45 lands on July 4, 2026.
Your return window closes July 4, 2026. Letting the tool jump across the month boundary avoids the easy mistake of assuming '45 days' is simply 'a month and a half'.
Tips & common mistakes
Decide up front whether you want an inclusive or exclusive count, because it changes the answer by one day. If someone says 'within 30 days', does day one start today or tomorrow? For legal and contractual deadlines this single day can matter, so confirm the convention before you rely on the number.
Don't forget leap years, which add February 29 every four years (with the odd century exception). Over multi-year spans they quietly accumulate, so hand-counting long periods almost always drifts. Letting the calculator handle it removes that error entirely.
When the result drives a real deadline, also consider time zones and business days. 'Five days from now' may mean five calendar days or five working days depending on context, and a deadline can land on a weekend or holiday. For shipping, contracts, and filings, check whether weekends count, and build in a buffer rather than aiming for the last possible day.
Frequently asked questions
Last reviewed: June 2026
About this calculator
Calculate days between two dates, add or subtract days from a date, and find the day of the week.