Date & Time Calculator

Add or subtract days, weeks, months, years, hours, minutes, or seconds from any date or time

Input

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Output

Output will appear here...

What is Date & Time Calculator

Written by Giorgos Kostas. Last reviewed: April 18, 2026

Date & Time Calculator performs arithmetic on ISO dates (YYYY-MM-DD) or datetimes (YYYY-MM-DDTHH:MM), adding or subtracting years, months, weeks, days, hours, minutes, or seconds.

Output includes the resulting timestamp in ISO 8601, the numeric difference in days, and the difference in milliseconds for scripting.

Why use it

Compute project deadlines quickly.
Check licence or contract renewal dates.
Add intervals when planning release trains.
Verify token expiry windows.
Preview time-zone-neutral ISO output for API payloads.

Features

Add / subtract year, month, week, day, h/m/s
ISO 8601 UTC input and output
Difference in days and milliseconds
Date & Time never leaves your machine
Leap-year aware

How to use Date & Time Calculator

Write the expression. Format: 'YYYY-MM-DD + N days' or '2026-04-18T12:00 - 3 hours'.
Click Run. The calculator returns start, operation, result, and difference.
Copy result. Use the ISO timestamp in your system.

Example (before/after)

Input

2026-04-18 + 60 days

Result

Start:     2026-04-18T00:00:00.000Z
Operation: +60 days
Result:    2026-06-17T00:00:00.000Z
Diff:      60.0000 days (5,184,000,000 ms)

Common errors

Invalid date

Non-ISO dates may not parse.

Fix: Use ISO 8601 (YYYY-MM-DD or YYYY-MM-DDTHH:MM).

Unsupported unit

Only year / month / week / day / hour / minute / second are supported.

Fix: Pick one of those units.

FAQ

Which units are supported?

year, month, week, day, hour, minute, second (plural forms accepted).

Does it handle time zones?

Input is treated as UTC and results are ISO 8601 UTC.

Does it handle leap years?

Yes — JavaScript's Date handles leap years automatically.

Can I compute a difference between two dates?

Use the 'days between dates' tool for that scenario.

Is input uploaded?

No — arithmetic runs in your browser.

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