Drug Half-Life Calculator

Your details

The amount of drug administered at time zero, in milligrams.
mg
Time for the drug concentration to fall by exactly half. Enter in the unit you select below.
Unit for the half-life value entered above.
How much time has passed since the dose was taken. Use the same unit as the half-life.
Drug remainingBelow 50%, still detectable
125mg

Amount of the original dose still present in the body at the elapsed time.

Concentration remaining25%
Half-lives elapsed2
Time to 50% elimination6
Time to 95% elimination25.93
Time to 99% elimination39.86
25% remaining
Cleared (>99%)<1%Nearly clear (>95%)1%-5%Partially cleared5%-50%Most still present50%+

25.0% of the dose (125.00 mg) remains after 12 hours.

  • After 12 hours, 125.00 mg (25.0%) of the original 500 mg dose is still present.
  • 2.0 half-lives have passed. Each half-life halves what remains.
  • The drug will reach 95% elimination in about 25.9 hours total (roughly 4.3 half-lives).
  • Full practical clearance (99%) is reached around 39.9 hours after the dose (about 6.6 half-lives).

Next stepMost of the dose has cleared, but detectable levels may persist. Check with your pharmacist about drug-interaction windows.

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