Add or Subtract Days Calculator
Move a calendar date forward or back by whole days.
Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
Example Calculation
- Start date: 2026-01-01
- Days to add: 30
Adding 30 days to 1 January 2026 gives 31 January 2026.
Frequently asked questions
How do I use this calculator?
Enter start date, days to add. The result updates automatically. Use Reset to restore the example values.
What method does it use?
New date = start date + signed day count. Follow the units and definitions shown with the inputs to apply this relationship consistently.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.