Date and Time Addition and Subtraction
Choose Add or Subtract for whole years, months, days, hours, minutes and seconds. Add is the default; negative values reverse the selected operation.
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Choose Add or Subtract for whole years, months, days, hours, minutes and seconds. Add is the default; negative values reverse the selected operation. Month ends are clamped. Use local dates and check UTC around daylight-saving changes.
Date and Time Addition and Subtraction
Add whole years, months, days, hours, minutes and seconds to a local date and time, with month-end clamping.
Date and Time Addition and Subtraction
The form starts with the browser's current local date and time. Six whole-number fields add calendar years, calendar months, days, hours, minutes and seconds; defaults are 0 years, 0 months, 1 day and zero for the time fields. Blank adjustment fields act as zero. Decimal, nonfinite and out-of-range values are rejected; use whole numbers.
Years and months are applied first in local time with end-of-month clamping, then days, hours, minutes and seconds are applied in that order. For example, 2024-01-31 10:30 plus one month and zero days becomes 2024-02-29 10:30, not a March rollover. Leap day 2024-02-29 plus one year becomes 2025-02-28.
Verified mixed-unit example: 2025-12-31 23:30 plus 0 years, 0 months, 1 day, 2 hours and 45 minutes becomes 2026-01-02 02:15 in the browser's local timezone. Negative field values reverse the selected operation for that unit.
The result displays the browser-local date and time, an ISO 8601 UTC value and a UTC text value. A datetime-local input has no named timezone or UTC offset; daylight-saving transitions follow the browser and operating system timezone rules, so adding one calendar day can represent 23, 24 or 25 elapsed hours.
Choose the local starting date and time, set only the units you need, press Add to date and verify the local and UTC lines. The calculation runs in the browser and does not include holidays, business-day rules, recurring schedules, timezone conversion or historical-calendar guarantees. For deadlines across jurisdictions, confirm the intended timezone separately.
The Days field starts at 1. Set it to 0 when adding only months or time. Use whole numbers: |years| ≤ 10,000, |months| ≤ 120,000, and each other unit ≤ 1,000,000 in absolute value. Blank fields act as 0; decimals and out-of-range values are rejected. Use a four-digit starting year, 0001–9999. A larger year offered by a browser picker is not accepted by the current parser. The computed result must also stay within the JavaScript Date range.
Processing takes place locally in your browser.