Pindrop

Half-Life Visualizer

See how a medication builds up with repeat dosing: the level over time, how long until it reaches steady state, and how far it swings between shots.

mg

Semaglutide: half-life ~7.0 days, peak at 34h.

0.00000.631.251.882.50StartW1W2W3W4W5W6W7W8mg-equivalent level
Steady-state peak
1.79mg-eq
Trough
1.03mg-eq
Trough vs peak
58%
Time to steady state
~5wks

Population-average pharmacokinetic model. Individual variation is significant. Levels are shown in dose-equivalent units, not blood concentration. Not medical advice.

What this calculator does

When you dose a medication before the last dose has fully cleared, the levels stack. Each injection adds to what is still in your system, and the curve climbs week over week until intake and clearance balance out. That balance point is called steady state. This tool plots that build-up so you can see it instead of guessing at it.

Pick a compound and its published half-life and time-to-peak load automatically. Set your dose, how often you inject, and how many weeks to show. The curve uses a standard one-compartment absorption model, the same shape pharmacology uses to describe a drug rising to a peak and then tailing off, repeated for every dose and summed.

Reading the result

The line is your estimated level over time; the small marks along the bottom are injections. The shaded band shows the peak-to-trough range once you reach steady state. The stats give the steady-state peak and trough, how deep the level dips between shots as a percentage, and roughly how many weeks until you plateau, which is about five half-lives. Levels are in dose-equivalent units to show the shape and timing, not a blood concentration, and everyone clears drugs at a different rate.

Common questions

What is a drug half-life?
Half-life is the time your body takes to clear half of a dose. If a drug has a 24-hour half-life, half is gone in a day, three-quarters in two days, and so on. It sets how fast a drug builds up and how long it lingers after you stop.
How many half-lives does it take to reach steady state?
About 5. After five half-lives, the amount going in each dose roughly matches the amount your body clears, so levels flatten out. This calculator models that buildup so you can see when you are getting close.
How long until semaglutide reaches steady state?
Semaglutide has a half-life of about 7 days, so at five half-lives it takes roughly 4 to 5 weeks of weekly dosing to level off. That is why titration schedules move slowly and why the full effect of a dose change takes weeks to show up.
When do testosterone levels stabilize after starting TRT?
It depends on the ester. Testosterone cypionate and enanthate have half-lives around 5 to 8 days, so levels steady out in about 4 to 6 weeks. That is the usual reason bloodwork gets checked near the 6-week mark, once things have settled.
Why do drug levels build up over weeks instead of right away?
Because you add the next dose before the last one fully clears. Each dose stacks on the leftover from the ones before it until intake and clearance balance out. The longer the half-life, the more doses stack and the longer that buildup takes.
What are peak and trough levels?
Peak is the highest level right after a dose, and trough is the lowest, right before the next one. More frequent, smaller doses keep peak and trough closer together, which means steadier levels. Big swings between them are why some people split their doses.

Pindrop is a calculation tool, not medical advice. Confirm your dose and protocol with a licensed healthcare provider.