Caffeine Half-Life Clearance

Caffeine t½ ≈ 5 hr in adults. Dose × 0.5^(hours/5) = remaining.

Inputs

Avg adult: 5 hr. Smokers: 3 hr. Pregnant: 9-15 hr. Hormonal birth control: 8-10 hr.

Result

Loading calculator…
—

General calculation reads

Amazon affiliate
How Not to Be Wrong
Jordan Ellenberg - math thinking
Shop on Amazon
The Joy of X
Steven Strogatz - accessible math
Shop on Amazon
Scientific calculator (Casio fx-991EX)
Shop on Amazon

As an Amazon Associate we may earn from qualifying purchases. This does not add cost for you.

How to use this calculator

  • Enter dose mg + hours since.
  • Adjust half-life if you know yours.

About this calculator

Caffeine half-life is ~5 hours in healthy adults — meaning a 400mg dose at 8 AM leaves 200mg by 1 PM, 100mg by 6 PM, 50mg by 11 PM (still affects sleep!). Half-life varies: smokers 3 hr (induce CYP1A2), pregnant women 9-15 hr (third trimester), hormonal birth control users 8-10 hr. To protect sleep: stop caffeine 6-10 hours before bed. Sources: NIH; Mandel (2002).

Frequently asked

Why does sleep matter?+
Even small caffeine (50mg) blocks adenosine receptors → reduces deep sleep. Cumulative across days = chronic sleep debt.
Common doses?+
Cup brewed coffee: 95-200 mg. Espresso shot: 60-75 mg. Tea: 25-50 mg. Energy drink: 80-300 mg. Pre-workout: 200-400 mg.
Tolerance?+
Builds in 1-2 weeks regular use. Doesn't affect half-life — only psychological alertness.
Genetic variation?+
CYP1A2 fast-metabolizers (~½ of population) clear in 4 hr. Slow: 6+ hr. Only 23andMe-style tests confirm.
When to cut off?+
Stop 8-10 hr before bed for noticeable sleep improvement. Sensitive sleepers: 12+ hr.

Related calculators

Daily Protein by Body Weight
Daily protein need = body weight × g/kg target. RDA 0.8 g/kg; athletic 1.6-2.2 g/kg.
Daily Water Intake
Base 0.5 oz/lb (33 mL/kg) + 12 oz per 30 min exercise.
Creatine Loading + Maintenance
Loading: 0.3 g/kg/day for 5-7 days. Maintenance: 0.03 g/kg/day (~3-5g).
Daily Sodium Target
AHA limit: 1500 mg ideal, 2300 mg max. Athletes lose 500-1500 mg/hr in sweat.
Rest Day / Recovery Calculator
Recommended rest days = base + intensity adjustment − sleep credit + age adjustment.
Half-Life ↔ Decay Constant
t½ = ln(2) / k. Convert between half-life and decay constant; predict remaining fraction.

More tools you might like

Hand-picked tools that pair well with this one — same audience, same intent.

Half-Life ↔ Decay Constant
Calc

t½ = ln(2) / k. Convert between half-life and decay constant; predict remaining fraction.

Rest Day / Recovery Calculator
Calc

Recommended rest days = base + intensity adjustment − sleep credit + age adjustment.

Daily Protein by Body Weight
Calc

Daily protein need = body weight × g/kg target. RDA 0.8 g/kg; athletic 1.6-2.2 g/kg.

Daily Water Intake
Calc

Base 0.5 oz/lb (33 mL/kg) + 12 oz per 30 min exercise.

Creatine Loading + Maintenance
Calc

Loading: 0.3 g/kg/day for 5-7 days. Maintenance: 0.03 g/kg/day (~3-5g).

Life Insurance Beneficiary Claim
Docs

Letter and supporting documents for a beneficiary to claim life-insurance proceeds after the insured's death.