About Date Calculator

What this is

Date Calculator is a small collection of free tools for working with dates: finding the difference between two dates, adding or subtracting time, calculating an exact age, and counting business days. It is part of the simtool.dev family of simple, single-purpose utilities.

Privacy

Everything runs entirely in your browser. There is no backend and no database — the dates you enter never leave your device. Your inputs are stored only in your browser’s local storage so they are still there when you come back.

How the math works

All date arithmetic is performed on calendar dates in UTC, which avoids the off-by-one errors that time zones and daylight saving time can otherwise introduce. Month and year additions clamp to the last valid day of shorter months (so January 31 plus one month is the end of February). The logic is covered by an automated test suite.

Disclaimer

• Provided “as is” for general informational purposes.
• Business-day calculations exclude weekends only; public holidays are not subtracted.
• For legal, financial, or medical deadlines, please verify results independently.

Contact

Questions or feedback? Email [email protected].