Date Difference Calculator
Count the days, weeks, hours and the years, months and days between two dates, or add and subtract days, weeks, months or years from any date.
Date Difference Calculator — Pick a start and end date to see the total number of days between them, a years-months-days breakdown, and the total weeks and hours. A second mode adds or subtracts days, weeks, months or years from any date to find the resulting date. Every calculation runs locally in your browser — no dates are ever sent to a server.
What is Date Difference Calculator?
A date difference calculator that measures the span between two dates and does date math, entirely in your browser. In Difference mode you enter a start and end date and it shows the total number of days, a calendar breakdown in years, months and days, and the total weeks and hours between them; if the end date is earlier than the start the result is shown as a negative span. In Add / subtract mode you enter a base date, an amount and a unit (days, weeks, months or years) and it returns the resulting date — a negative amount subtracts. Dates are computed in UTC so day, week and hour counts are not skewed by daylight-saving changes. Project managers, contract and lease administrators, students counting down to a deadline, and anyone working out an age, a due date, or a notice period use it to answer "how many days between" and "what date is N days from now."
How to use Date Difference Calculator
- Choose a mode: Difference (between two dates) or Add / subtract (date math).
- In Difference mode, pick a start date and an end date with the two date pickers.
- Read the results: total days, the years-months-days breakdown, and the total weeks and hours.
- For date math, switch to Add / subtract and pick a base date.
- Enter an amount and choose a unit (days, weeks, months or years); a negative amount subtracts.
- Read the resulting date in the result field.
Examples
Days between two dates
Input
Start 2026-01-01, End 2026-06-17
Output
Total days 167 · 0 years, 5 months, 16 days · 23 weeks · 4008 hours
Add 90 days to a date
Input
Base 2026-06-17, amount 90, unit days
Output
2026-09-15
Subtract with a negative amount
Input
Base 2026-06-17, amount -2, unit weeks
Output
2026-06-03
Frequently asked questions
- What does the result include?
- In Difference mode you get the total number of days, a years-months-days breakdown (for example 0 years, 5 months, 16 days), the total number of whole weeks, and the total hours. In Add / subtract mode you get a single resulting date.
- Can I count backwards or subtract?
- Yes. If the end date is earlier than the start date, Difference mode shows a negative span (marked with a minus sign). In Add / subtract mode, entering a negative amount subtracts that many days, weeks, months or years from the base date.
- How are months and years counted?
- The years-months-days breakdown follows the calendar — it borrows the real number of days in the previous month and accounts for leap years, so it matches how people read a span like "2 months and 5 days" rather than dividing by a fixed 30 days. Adding months or years lands on the same day-of-month where possible.
- Does it use my timezone?
- Dates are calculated in UTC at midnight, so the day, week and hour totals stay exact and are never thrown off by daylight-saving time changes or your local timezone offset.
- Are my dates uploaded anywhere?
- No. Every calculation runs locally in your browser — no dates are sent to any server and there is no upload, so it works offline and keeps your data private.
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