Time Duration Calculator
Adjust the inputs below. Results update as you type.
How it works
Duration accounts for varying month lengths and leap years. Common uses: age calculation, contract term verification, and billing period calculation. ISO 8601 duration format: P1Y2M3DT4H5M6S (1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds). Legal and financial contracts often use specific day-count conventions (actual/actual, 30/360)—confirm which applies.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Duration = end datetime − start datetime. Convert both to a common unit (minutes or seconds), subtract, then express the result in days, hours, and minutes.
Worked example
From 9:15 AM to 5:45 PM is 8 hours 30 minutes; across dates, the day difference is added in too.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
How do I find the time between two moments?+
Convert both to a common unit such as minutes since a reference, subtract, and convert the difference back to days, hours, and minutes.
Does it handle dates and times together?+
Yes. Including both dates and clock times accounts for spans that cross midnight or multiple days.
What about daylight saving changes?+
A spring-forward or fall-back day is 23 or 25 hours long, so durations across the change can be an hour off if time zones are ignored.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.