DateCalculator Free Online Date Calculator

Q: How to add or subtract days from a date?

Choose the Add or Subtract Duration mode, pick a start date (it defaults to today), select Add (+) or Subtract (−), and enter any number of years, months, weeks or days. DateCalculator instantly shows the exact target date, its day of the week, whether it falls in a leap year and whether it is a business day.

Q: How are leap years handled in date calculations?

DateCalculator uses the native JavaScript calendar, which follows the Gregorian rules: a year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. February 29 is counted automatically, and when you add years or months to a date like January 31 or February 29, the result is clamped to the last valid day of the target month (for example, February 28 in a non-leap year).

Q: How do I calculate the exact number of days between two dates?

Open the Days Between Two Dates mode and pick a start and end date. You get the total number of days, the same span as weeks plus days, as years, months and days, plus the number of business (Monday–Friday) days. Tick “Include end date” if you want both the first and last day counted.

Q: What happens when I add a month to January 31?

Because February has no 31st day, the result is clamped to the last day of February: February 28, or February 29 in a leap year. This end-of-month rule matches how banks, spreadsheets and most calendar apps handle month arithmetic.

Q: How are business days calculated?

Business days are Monday through Friday. Saturdays and Sundays are excluded. Public holidays vary by country and are not subtracted, so adjust for local holidays if needed.

100% Free, Secure & Browser-Based Date Calculator & Duration Tool.

Add or Subtract Duration

Pick a start date, choose an operation and enter a duration.

Start date

Operation

Years

Months

Weeks

Days

Quick presets

Count days as business days (skip weekends for the Days & Weeks part)

Target date

—

Select a date

Days from start: 0
Relative to today: —
Day of year: —
ISO week: —

Instant results as you type
Private — nothing leaves your browser
Leap-year & month-end accurate

How to use the Free Online Date Calculator

DateCalculator answers two everyday questions: “What date will it be after (or before) a certain amount of time?” and “How many days are there between two dates?” It works for deadlines, notice periods, project schedules, pregnancy and due dates, warranty and contract terms, visa stays, subscription renewals and anything else that depends on the calendar.

Add or subtract days, weeks, months & years

Pick a start date (defaults to today).
Choose + Add or − Subtract.
Enter years, months, weeks and/or days — or tap a preset.
Read the target date, weekday, leap-year and business-day status.

Count days between two dates

Switch to Days Between Dates.
Pick a start date and an end date.
Optionally include the end date in the count.
See total days, weeks + days, years/months/days and business days.

How the date math works

Order of operations

Years and months are applied first, then weeks and days. This is the same order used by spreadsheets and calendar apps, so results match what you expect.

Month-end clamping

Adding 1 month to Jan 31 gives Feb 28 (or Feb 29 in a leap year) — never an overflow into March.

Time-zone safe

Day counts use calendar dates in UTC, so daylight-saving shifts never add or lose a day.

Common date calculations

Question	How to do it
What date is 90 days from today?	Add mode → tap +90 Days
What was the date 6 months ago?	Add mode → − Subtract → Months = 6
Deadline in 10 working days?	Days = 10 and tick business days
How many days until the end of the year?	Between mode → Start = Today → End of Year
How many weeks between two dates?	Between mode → read the Weeks + days row

Frequently Asked Questions

How to add or subtract days from a date?

Choose the Add or Subtract Duration mode, pick a start date (it defaults to today), select Add (+) or Subtract (−), and enter any number of years, months, weeks or days. DateCalculator instantly shows the exact target date, its day of the week, whether it falls in a leap year and whether it is a business day.

How are leap years handled in date calculations?

DateCalculator follows Gregorian calendar rules: a year is a leap year if it is divisible by 4, except century years, which must be divisible by 400 (so 2000 was a leap year but 2100 will not be). February 29 is counted automatically, and when you add years or months to dates like January 31 or February 29, the result is clamped to the last valid day of the target month.

How do I calculate the exact number of days between two dates?

Open the Days Between Two Dates mode and pick a start and end date. You get the total number of days, the same span expressed as weeks plus days and as years, months and days, plus the number of business (Monday–Friday) days. Tick “Include end date” if you want both the first and the last day counted.

What happens when I add a month to January 31?

February has no 31st, so the result is clamped to the last day of February: February 28, or February 29 in a leap year. This end-of-month rule matches how banks, spreadsheets and most calendar apps handle month arithmetic.

How are business days calculated?

Business days are Monday through Friday; Saturdays and Sundays are excluded. Public holidays differ by country and are not subtracted, so adjust for local holidays if needed.

Is DateCalculator free and private?

Yes. DateCalculator is 100% free, needs no sign-up, and every calculation runs locally in your browser. No dates are ever sent to a server.