Tea Caffeine by Steep Time Calculator
Estimate how much caffeine a cup of tea holds based on the tea type and how long you steep it, using a first-order extraction model.
How it works
Extracted fraction = 1 − e^(−t ÷ τ), τ ≈ 2.2 min · Caffeine = type maximum × fraction
Caffeine leaves the leaf fast at the start of a steep and then tapers off, which a first-order extraction curve captures well: the fraction released is 1 − e^(−t/τ), with a time constant around two minutes. Most of the caffeine is out within the first few minutes, so a longer steep adds flavor and tannins more than it adds caffeine. The ceiling depends on the tea — black and oolong hold more than green and white — and the figures here are per-cup estimates, not lab values.
Worked example
Black tea tops out near 55 mg per cup. Steeping 4 minutes releases 1 − e^(−4/2.2) ≈ 84% of that, so about 46 mg — while a 2-minute steep gives only ~60%, roughly 33 mg.
Frequently asked questions
Does longer steeping mean much more caffeine?
Not proportionally. Because extraction tapers, most caffeine comes out in the first two to three minutes. Going from 3 to 6 minutes adds relatively little caffeine but a lot more tannin and bitterness.
Which tea has the most caffeine?
Among these, black and oolong generally sit highest, with green and white lower. The exact amount varies a lot by leaf, quantity and water temperature, so treat the type maximums as typical rather than fixed.
Can I decaffeinate tea by steeping and dumping the first cup?
Only partly. A 30-second rinse removes some caffeine but far less than the myth suggests — most caffeine survives a short rinse. It is a modest reduction, not true decaffeination.
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This calculator is for educational purposes. Double-check important results before acting on them.