A medication half-life calculator shows how long a drug stays in your system by modeling concentration decay over time. The half-life is the time it takes for half of the drug to be eliminated from your body. After 5 half-lives, approximately 97% of the drug has been cleared. Enter a medication or custom half-life below to visualize the elimination curve.
Educational Use Only
This calculator shows theoretical pharmacokinetics for educational purposes only. Actual drug metabolism varies by individual factors including age, weight, liver function, and genetics. Consult your healthcare provider for medical advice.
Drug Parameters
Concentration Over Time
Elimination Timeline
| Half-Lives | Time | Remaining | Eliminated |
|---|
Steady-State Information
For educational purposes only. This calculator shows theoretical pharmacokinetics. Actual drug metabolism varies by individual factors including age, weight, liver function, and genetics. Consult your healthcare provider for medical advice.
Common Drug Half-Lives
Typical half-life values from clinical literature. Individual values may differ. Formula: C(t) = C₀ × (0.5)t/t½
| Drug | Brand Name | Half-Life | Cleared (5 HL) |
|---|---|---|---|
| Ibuprofen | Advil, Motrin | 2-4 h | 10-20 h |
| Acetaminophen | Tylenol | 2-4 h | 10-20 h |
| Aspirin | Bayer | 3-5 h | 15-25 h |
| Amoxicillin | Amoxil | 1-1.5 h | 5-7.5 h |
| Metformin | Glucophage | 4-8.7 h | 20-44 h |
| Lisinopril | Zestril | 12 h | 60 h |
| Atorvastatin | Lipitor | 14 h | 70 h |
| Omeprazole | Prilosec | 0.5-1 h | 2.5-5 h |
| Levothyroxine | Synthroid | 168 h (7 d) | 840 h (35 d) |
| Sertraline | Zoloft | 26 h | 130 h |
| Fluoxetine | Prozac | 48-72 h | 10-15 d |
| Alprazolam | Xanax | 6-12 h | 30-60 h |
| Melatonin | — | 0.5-1 h | 2.5-5 h |
| Caffeine | — | 3-5 h | 15-25 h |
| Semaglutide | Ozempic, Wegovy | 168 h (7 d) | 840 h (35 d) |
How to Use the Medication Half-Life Calculator
Understanding a drug's half-life helps you know how long a medication stays active in your body. This medication half-life calculator uses the standard pharmacokinetic formula C(t) = C₀ × (0.5)t/t½ to model concentration decay over time, showing you when a drug is effectively eliminated.
Step 1: Select a Medication or Enter a Custom Half-Life
Choose from 15 common medications with pre-loaded half-life values, organized by category. If your medication is not listed, select "Custom half-life" and enter the value in hours. Your pharmacist or the drug's prescribing information can provide this number.
Step 2: Enter the Dose Amount
Enter the dose in milligrams. This is used to calculate absolute concentration values at each time point. For example, 400 mg of ibuprofen or 500 mg of acetaminophen. The dose affects the concentration values shown but not the elimination timeline, since half-life is independent of dose.
Step 3: Choose Single or Repeated Dosing
For a single dose, the calculator shows simple exponential decay. For repeated dosing, enter the interval between doses and the number of doses. The calculator then models drug accumulation — each new dose adds to the remaining concentration from previous doses, eventually reaching a steady state.
Understanding the Results
The concentration chart shows how drug levels change over time. For single doses, you see a smooth decay curve. For repeated doses, you see a sawtooth pattern as each dose boosts the concentration before it decays again. The elimination table shows milestones at each half-life — after 5 half-lives, 96.875% of the drug has been eliminated and it is considered effectively cleared from your system.
Steady State and Accumulation
When taking a medication repeatedly, the concentration gradually builds up until it reaches steady state — the point where the amount entering equals the amount being eliminated. The accumulation factor tells you how much higher steady-state levels are compared to a single dose. Steady state is typically reached after approximately 5 half-lives of regular dosing.
FAQ
Is this medication half-life calculator free?
Yes, this calculator is completely free with no signup or limits. All calculations run locally in your browser. You can calculate drug elimination times as many times as you need.
Is my data safe and private?
Yes, all calculations run entirely in your browser using client-side JavaScript. No medication information or personal data is sent to any server or stored anywhere. Your data stays on your device only.
What is a drug half-life?
A drug's half-life is the time it takes for the concentration of the drug in your body to reduce by half. For example, if a drug has a 4-hour half-life, after 4 hours only 50% remains, after 8 hours only 25% remains, and so on.
How many half-lives until a drug is eliminated?
A drug is considered effectively eliminated after 5 half-lives, when 96.875% has been cleared from the body. For a drug with a 4-hour half-life, this means about 20 hours. Only 3.125% of the original dose remains after 5 half-lives.
What is steady-state concentration?
Steady state occurs when the amount of drug entering the body equals the amount being eliminated, creating a stable concentration range. This typically takes about 5 half-lives of regular dosing to achieve. At steady state, drug levels fluctuate predictably between doses.
Why do some drugs have a range for half-life?
Drug half-lives vary between individuals due to factors like age, weight, liver function, kidney function, genetics, and interactions with other medications. The ranges shown represent typical values from clinical studies. Your actual half-life may differ.
Is this a substitute for medical advice?
No. This calculator shows theoretical pharmacokinetics for educational purposes only. Actual drug metabolism varies by individual factors including age, weight, liver function, and genetics. Always consult your healthcare provider for medical advice about your medications.