Add Days to a Date
Add days, weeks, months or years to a date. Free, and runs entirely in your browser — nothing you enter is uploaded, stored or sent to a server.
About Date Calculator
Three questions in one tool: how far apart are two dates, what date is a given interval after this one, and what date is that interval before it. Differences are reported in several units, including business days, which is the number contracts and SLAs usually mean.
Adding months and years is where hand calculation goes wrong, because month lengths differ. Adding one month to 31 January cannot produce 31 February, so the date rolls into March — worth seeing explicitly before it becomes a billing bug.
Where it helps
- Difference, addition and subtraction without opening a spreadsheet.
- Business-day counts for deadlines that ignore weekends.
- Handles months and years, not just fixed-length days.
- Leap years are accounted for automatically.
Limits
- Business days exclude weekends but know nothing about public holidays, which vary by country.
- Month arithmetic rolls over rather than clamping: adding one month to 31 January lands in March, because February has no 31st.
- Calculations use calendar dates, so a range spanning a daylight saving change is not exactly 24 hours per day.
- Differences are reported in whole days, so a gap of a few hours shows as 0 days rather than being rounded up.
Frequently asked questions
Are public holidays excluded from business days?
No — only Saturdays and Sundays. Holidays differ by country and region, so subtract them yourself.
What does adding a month to 31 January give?
3 March in a normal year — the date rolls past the end of February rather than clamping to the 28th. When end-of-month behaviour matters, add days instead.
Is the end date included in a difference?
The difference is exclusive: from Monday to Friday is four days. Add one if you are counting days inclusively.
Can I work with times as well as dates?
Yes — include a time in the input, and use hours or minutes as the unit.
Related tools
- Unix Timestamp — Convert between timestamps, ISO dates and local time
- Timezone Converter — Convert a moment between time zones
- Cron Expression Viewer — Explain a cron schedule and list the next runs
- Percentage Calculator — Percentages, differences and percentage change
- Duration Converter — Convert between ISO 8601 durations, seconds, clock time and plain words
More Date & Time tools
- Unix Timestamp — Convert between timestamps, ISO dates and local time
- Timezone Converter — Convert a moment between time zones
- Date Calculator — Difference between dates, or add and subtract time
- Cron Expression Viewer — Explain a cron schedule and list the next runs
- Duration Converter — Convert between ISO 8601 durations, seconds, clock time and plain words