Date Calculator
Add or subtract years, months, weeks and days from any date to find the resulting date — computed entirely in your browser.
The Date Calculator runs entirely in your browser. The start date and amounts you enter are used only for the on-device calculation and never leave your machine or reach ArrayKit.
Open the Date Duration Calculator
About Date Calculator
The Date Calculator takes a start date and adds or subtracts a mix of years, months, weeks and days to give you the exact resulting date. Pick the date, choose Add or Subtract, then fill in as many of the four amount fields as you need — the answer updates as you type. Month and year math clamps to the end of the month, so January 31 plus one month lands on February 28 (or 29 in a leap year) rather than spilling into March. Alongside the resulting date you get its weekday, the total number of calendar days moved, and how many of those are business days versus weekend days. Use it to find a deadline, a warranty or notice-period end date, a due date, or simply "90 days from today." Every calculation runs on your device — the dates you enter never leave your browser.
Features
- Add or subtract years, months, weeks and days in one pass
- Month and year math clamps to the end of shorter months
- Shows the resulting date plus its day of the week
- Total calendar days moved, split into business and weekend days
- Add and Subtract toggle without re-typing the amounts
- Today shortcut to seed the start date instantly
- Copy the result as YYYY-MM-DD or as a full written date
- Runs entirely in your browser with no dates sent anywhere
How to use the Date Calculator
- Pick a start date, or tap Today to use the current date
- Choose Add or Subtract with the Operation toggle
- Enter any of years, months, weeks and days to apply
- Read the resulting date, its weekday and the day counts
- Copy the result as YYYY-MM-DD or a full written date
Example
Input
Start: 2025-01-31
Add: 1 month, 1 day
Output
2025-03-01 (Saturday)
Total days: 29 · Business days: 21
Months clamp first (Jan 31 → Feb 28), then the extra day lands on March 1.
Common errors & troubleshooting
- Adding one month to January 31 gives February 28, not March 2. — That is intentional. Month math clamps to the last valid day of the target month, matching how spreadsheets (EDATE) and most calendars add months.
- You want to go back in time but the amount fields only take positive numbers. — Switch the Operation toggle to Subtract. The same year/month/week/day amounts are then applied backwards from the start date.
- The total days figure looks larger than expected for a whole year. — A span crossing February 29 is 366 days, not 365. The resulting date is still exactly one year on; only the day count reflects the leap day.
- The business-day count ignores a public holiday. — The split counts only Saturdays and Sundays as non-working. Regional holidays vary, so deduct any weekday holidays for your country separately — or use the Business Days Calculator.
Frequently asked questions
- How does the Date Calculator add months to a date?
- It applies years and months first as a calendar step, clamping the day to the target month's length, then adds any weeks and days. So January 31 plus one month is February 28 (February 29 in a leap year), and adding a further day lands on March 1.
- Can I subtract time to find an earlier date?
- Yes. Set the Operation toggle to Subtract and enter the years, months, weeks and days to go back. The tool applies the same amounts in reverse and shows the earlier resulting date and its weekday.
- In what order are years, months, weeks and days applied?
- Years and months are applied first (with end-of-month clamping), then weeks and days are added as a fixed 7-day and 1-day count. This ordering matches common date libraries and spreadsheet EDATE-plus-day arithmetic.
- What is the difference between total days and business days here?
- Total days is the whole calendar-day distance between the start and resulting date. Business days counts only the Mondays through Fridays in that span; weekend days counts the Saturdays and Sundays. Public holidays are not deducted.
- How do I calculate a date a number of days from today?
- Tap Today to set the start date, keep Add selected, and enter the number of days (or weeks, months, years). The resulting date — for example 90 days from today — appears immediately with its day of the week.
- Are the dates I enter sent anywhere?
- No. The Date Calculator runs entirely in your browser and computes everything on your device. The start date and the amounts you type never leave your machine or reach ArrayKit.
Related tools
- Date Duration Calculator — Calculate the duration between two dates in years, months, weeks, days and business days.
- Business Days Calculator — Add or subtract working days from a date, or count business days between two dates.
- Age Calculator — Calculate exact age in years, months and days as of any date, plus totals in weeks, days, hours and next birthday.
- Duration Converter — Convert a duration between seconds, minutes, hours, days, HH:MM:SS and human formats.
- Unix Timestamp Converter — Convert between Unix timestamps and human dates (local + UTC).
- World Clock & Time Zone Converter — Compare times across cities on an aligned 24-hour grid and plan meetings — right in your browser.
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