Date calculator · add or subtract days
Date calculator · add or subtract days: use start date, days to add · negative to subtract, count. Review the formula, worked example and calculation steps.
Inputs
Use the units shown—
Enter your values and select Calculate.
Formula & explanation
Move one calendar day at a time; optionally count weekdays only
Variables & units
- Start date
- Gregorian date
- Days to add · negative to subtract
- Numeric value · minimum -36600, maximum 36600
- Count
- Select an option
Worked example
2026-01-01 plus 30 calendar days is 2026-01-31.
Assumptions
Gregorian calendar. Weekday mode excludes only weekends and does not know local holidays.
Formula version 1.0.0. JavaScript floating-point arithmetic applies. Results display up to 6 decimal places; stored values retain available precision. Use the units shown.
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