Date Calculator

Q: How do I count the days between two dates?

Subtract the earlier date from the later one. This calculator counts the exact number of days, and can also show business days only (excluding weekends).

Q: How do I add days to a date?

Use the add/subtract mode and enter the number of days, weeks, months, or years to add or subtract. The calculator returns the resulting date and the weekday it falls on.

Q: Are business days different from calendar days?

Yes. Business days count only Monday through Friday, excluding weekends (and not accounting for public holidays). This calculator's business-day count skips Saturdays and Sundays.

Q: How do I calculate a legal or contractual notice period?

Add the specified number of days (or months) to the trigger date using the add/subtract tool. Read the contract carefully for whether it means calendar days or business days, and whether the start date itself counts as day one.

Q: Why does adding 30 days differ from adding 1 month?

30 days is a fixed count, while 1 month varies in length (28-31 days). Adding 1 month to January 15 gives February 15 (a 31-day gap that year), while adding 30 days to January 15 gives February 14 — one day earlier. The two only match exactly when the starting month has exactly 30 days.

Count the days between two dates, or add and subtract days, weeks, months, and years from any date.

Written by the Calculator Index team · Last reviewed September 2026

Days between two dates

Days between

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Weeks

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Business days

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Years & days

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Add or subtract from a date

Resulting date

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How date math works

The days-between count is the number of full days from the start date to the end date. Business days exclude Saturdays and Sundays (but not public holidays, which vary by country). When adding months or years, the calculator keeps the same day-of-month where possible, adjusting for shorter months (e.g., January 31 + 1 month lands on the last day of February).

Worked example

From Jan 1 to Dec 31, 2026 is 364 days (about 260 business days). Adding 90 days to July 22 gives October 20.

Worked example — a 60-day notice period

A lease requires 60 days' written notice starting March 15, 2026: 16 remaining days in March + 30 days in April + 14 days in May = 60 days, landing on May 14, 2026.

Everyday date questions

Handy for project deadlines, contract and notice periods, warranty windows, vacation planning, and "how many days until…" countdowns. For business-day-sensitive deadlines, remember this tool skips weekends but not holidays — check a holiday calendar for the exact working days. For someone's age specifically, the age calculator breaks it into years, months, and days; for durations in hours and minutes, use the time calculator.

Common notice and waiting periods

Purpose	Typical period
Apartment lease notice to vacate	30–60 days
Job resignation notice	2 weeks (10 business days)
Standard passport renewal	6–8 weeks
Visa processing (varies widely)	2–12 weeks
Home closing after contract	30–45 days

Common date-math mistakes

Counting the start date itself as "day one" inconsistently. Some contracts specify a notice period starting the day after delivery, not the day of — check the exact wording, since it can shift a deadline by a day.
Assuming "business days" excludes public holidays. This calculator's business-day count only skips Saturdays and Sundays, not holidays, so a period spanning a holiday will show one more available business day than actually exists.
Treating a "30-day" period as the same as one calendar month. A calendar month can be 28-31 days, which can shift a deadline by up to 3 days if the wrong unit is used for a fixed-day requirement.

Frequently asked questions

How do I count the days between two dates?

Subtract the earlier from the later. This tool also shows business days (weekends excluded).

How do I add days to a date?

Use add/subtract mode with days, weeks, months, or years.

Are business days different from calendar days?

Yes — business days count Mon–Fri only (holidays not excluded here).

How do I calculate a legal or contractual notice period?

Add the specified days or months to the trigger date, and check whether the contract means calendar or business days and whether the start date counts as day one.

Why does adding 30 days differ from adding 1 month?

30 days is fixed; a month varies (28-31 days). Adding 1 month to Jan 15 gives Feb 15; adding 30 days gives Feb 14.

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Last reviewed: September 2026.