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.
- UTC calendar dates only, not elapsed 30-day blocks. Clamping may make adding and then subtracting a month nonreversible.
Example Calculation
- Starting date: 2024-01-31
- Months to add or subtract: 1
31 January 2024 plus one calendar month becomes 29 February 2024.
Frequently asked questions
How do I use this calculator?
Enter starting date, months to add or subtract. The result updates automatically. Use Reset to restore the example values.
What method does it use?
Move to the target calendar month; clamp the day to its last valid day.. UTC calendar dates only, not elapsed 30-day blocks. Clamping may make adding and then subtracting a month nonreversible.
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.