The formula this calculator uses
Date Calculator
New date = Start date ± number of days
(calendar arithmetic handles month/year boundaries automatically)
Example: 2026-09-30 + 30 days → 2026-10-30
Everyday uses for a date calculator
Project deadlines, pregnancy due dates, notice periods, subscription renewals, and travel planning all need reliable date arithmetic. This tool does the addition or subtraction instantly without manual calendar counting.
How to use this calculator
- Enter the required values in the fields above.
- Results update automatically as you type.
- Adjust any input to explore different scenarios.
Frequently asked questions
Does it account for leap years?
Yes. JavaScript Date objects correctly handle leap years and varying month lengths.
Can I subtract days?
Yes. Enter a negative number (e.g. −14) to go backward.
What format should the date be in?
Use YYYY-MM-DD (ISO format) for reliable parsing.
How do I find days between two dates?
Use this tool twice or subtract the two Date objects in days; a dedicated “days between” mode can be added later.