Date Calculator
This calculator handles the two most common date questions: how many days, weeks or months lie between two dates, and what date results from adding or subtracting a span of time from a starting date — useful for deadlines, due dates, anniversaries and planning.
How to use the date calculator
- Choose whether you want the gap between two dates, or a new date from adding/subtracting time.
- For "days between", enter a start and end date — order does not matter, the result is always positive.
- For "add/subtract", enter a start date, an amount (use a negative number to subtract) and a unit, then read the resulting date.
Formula
Days between: the absolute difference between the two dates, in days, also shown as whole weeks and as a years/months/days breakdown.
Add/subtract: the start date shifted by the given number of days, weeks, months or years, handling different month lengths and leap years automatically.
Worked examples
Days until a deadline
From 1 January 2026 to 31 December 2026 is 364 days — useful for project planning or counting down to an event.
A due date 90 days out
Adding 90 days to 1 January 2026 lands on 1 April 2026 — the calculator accounts for January (31), February (28 in a non-leap year) and March (31) automatically.
Common real-world uses for date math
Beyond simple curiosity, date calculations come up in a few recurring practical situations:
- Deadlines and notice periods: "30 days from today" for a resignation notice period or a legal deadline.
- Due dates: a typical pregnancy due date is estimated as 280 days (40 weeks) from the first day of the last menstrual period — this calculator's "add" mode can project that directly.
- Project and event planning: counting back from a fixed event date to work out when preparation needs to start.
- Anniversaries and milestones: finding exactly how many days, weeks or years have passed since a specific date.
Note that this calculator counts calendar days, not working days — if you specifically need "business days" (excluding weekends and holidays), subtract roughly 2 days for every 7 calendar days as a rough estimate, since public holidays vary by state and country and aren't accounted for here.
Common mistakes to avoid
- Assuming every month is 30 days when adding "months" — the calculator adds calendar months (so 31 January + 1 month = 28/29 February, adjusted to the last valid day), not a flat 30-day block.
- Forgetting leap years when counting days across February in a leap year.
- Mixing up which date is the "start" when subtracting — for "days between", order does not matter, but for "add/subtract" the start date is always the one being shifted.
Frequently asked questions
How many days are between two dates?
Subtract the earlier date from the later one — this calculator does it automatically and also shows the total in whole weeks and as a years/months/days breakdown.
How do I add months to a date accurately?
Adding calendar months (not a fixed 30 days) means the day-of-month is preserved where possible, and adjusted to the last valid day of the target month when it does not exist (e.g. 31 January + 1 month lands on 28 or 29 February).
Can I subtract time from a date?
Yes — enter a negative number in the amount field (for example −14 days) to go backward from the start date.
Does this account for time zones?
No — this calculator works with calendar dates only, not specific times, so time-zone differences do not apply.
Reviewed September 29, 2026 by the CalcSolver editorial team. Found a mistake? Tell us; see our editorial policy.