How this calculator works
Convert both durations to a common time unit, then divide the first by the second. The result is dimensionless, so the chosen display units do not change the percentage. Reverse modes multiply by the percentage or divide by it. Months and years use the site's fixed average durations, rather than calendar date arithmetic.
Formula
p = t₁/t₂. t₁ = p × t₂. t₂ = t₁/p. The entered percentage number is 100p.
Worked example
Ninety minutes is 5400 seconds. Two hours is 7200 seconds. Their ratio is 0.75, so the first duration is 75% of the second. A quarter of one hour is 15 minutes.
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Frequently asked questions
Can the percentage exceed 100%?
Yes. Three hours compared with two hours is 150%.
Does this measure elapsed time between dates?
No. It compares durations. Calendar month lengths and daylight saving transitions are not included.
Can the reference duration be zero?
No. A percentage needs a positive reference duration. Zero time in the first duration is valid when that reference is positive.