Time & Date
Add or subtract days, weeks, months, or years from a date, or find the difference between two dates.
Result Date
Saturday, August 22, 2026
Saturday
Add or subtract time from a date. Leap years and month lengths are handled automatically.
A date calculator is a tool that performs two main functions: (1) Add/Subtract Mode—combines a start date with a duration (e.g., add 30 days to July 22, 2026) to show the resulting date and day of the week; (2) Difference Mode—compares two dates and returns the elapsed time in days, weeks, months, and years. It accounts for leap years, variable month lengths, and correctly identifies day-of-week names.
In Add/Subtract mode, you enter a start date, choose to add or subtract, specify a quantity, and select the unit (days, weeks, months, or years). The calculator adjusts the date accordingly and displays the result with the day of the week. In Difference mode, you provide two dates and the tool counts the calendar days, weeks, months, and years between them, accounting for partial months and leap years with proper borrowing logic.
Add/Subtract: result_date = start_date ± (quantity × unit). Difference: for each unit, count complete periods; borrow days from months, months from years as needed. Days between = absolute difference in milliseconds ÷ (1000 × 60 × 60 × 24).When adding/subtracting, the tool applies the operation to the start date's calendar units. Leap years (divisible by 4, except centuries not divisible by 400) shift February length, affecting any duration that crosses February. When finding differences, the tool counts complete units: it subtracts the earlier date from the later date field-by-field (years, then months, then days), borrowing when needed, ensuring no negative remainders.
| Input | Result | Notes |
|---|---|---|
| Start: 22 July 2026, Add 30 days | 21 August 2026 (Tuesday) | Adding 30 days to July 22 advances the date to August 21, falling on a Tuesday. |
| Start: 15 January 2026, Subtract 45 days | 01 December 2025 (Monday) | Subtracting 45 days from mid-January rolls back past New Year's into December 2025. |
| Date 1: 01 January 2020, Date 2: 01 January 2026 | 6 years, 0 months, 0 days (2192 days including leap day 2024) | Exactly 6 years apart; the span includes the leap year 2024, adding one extra day. |
Leap years occur every 4 years, except for century years (divisible by 100) unless also divisible by 400. February has 29 days in leap years, 28 otherwise. When you add/subtract across February or calculate differences spanning leap years, the tool counts the correct number of days and adjusts month/year boundaries accordingly.
If you add 1 month to January 31, the result is February 28 (or 29 in a leap year) because February has fewer days. The calculator respects month-end rules, avoiding invalid dates like February 30.
Yes. In Add/Subtract mode, choose 'Subtract' and set your quantity. The date will roll backward into earlier months, years, or even centuries if needed. In Difference mode, the order of dates doesn't matter; the tool reports the absolute span between them.
The calculator counts complete years, then remaining months, then remaining days with proper borrowing. For example, from January 31 to February 28 is 0 years, 0 months, 28 days (not 'one month minus 3 days').
No, it counts all calendar days. For business-day calculations, use a business-days-calculator tool that excludes weekends and holidays.
Yes. This calculator runs entirely in your browser; no dates are stored, sent, or logged to any server. Your data never leaves your device.