Time Calculator

How to Use Time Calculator

1. Pick a mode — Add, subtract, difference or unit conversion.
2. Enter the inputs — Base time plus hours/minutes/seconds, or a value plus from/to units.
3. Read the result — The Time Calculator displays the result, total minutes, total seconds, decimal hours and whether the result crosses a day.

Formula & Theory - Time Calculator

All clock arithmetic uses seconds-of-day:

toSeconds(h, m, s) = h * 3600 + m * 60 + s

Add / subtract:

result = baseSeconds ± durationSeconds
crossDay = result < 0 or result >= 86400
result   = ((result mod 86400) + 86400) mod 86400

Difference:

diff = endSeconds - startSeconds
crossDay = diff < 0
diff     = ((diff mod 86400) + 86400) mod 86400

Unit conversion uses these factors:

seconds → minutes: / 60
seconds → hours:   / 3600
seconds → days:    / 86400
minutes → seconds: * 60
hours   → seconds: * 3600
days    → seconds: * 86400

So the Time Calculator is a single tool for the most common time-related calculations.

Use Cases for Time Calculator

The Time Calculator is useful for:

• Scheduling — Add or subtract hours from a meeting time across time zones.
• Project tracking — Sum estimated durations to plan a delivery time.
• Education — Practise base-60 and base-24 time arithmetic.
• Sports — Convert times between minutes and hours for pacing.
• Programming — Quickly sanity-check seconds vs. milliseconds.
• Personal tasks — Calculate how long it has been since an event.

The Time Calculator runs entirely in your browser; no data is sent to a server.