OptiPin
Split dose calculator
Break a weekly dose into smaller, more frequent injections without changing the weekly total. Then see what it actually does to your peaks and troughs, which is the only reason to bother.
Every schedule at this weekly total
The same weekly amount, spread differently. Peaks and troughs are the estimated amount in your system once levels have settled, so the useful column is the last one: how far your levels travel between injections.
| Schedule | Per injection | Units | Peak (mg) | Trough (mg) | Swing |
|---|
Want the full curve rather than the endpoints? The half-life calculator plots build-up, steady state and washout for the same compound.
See the new schedule against your real data
OptiPin forecasts your levels from the doses you actually log, calibrates to your bloodwork, and keeps the reminder schedule in step when you change frequency. All on-device.
Download on the App StoreHow to use this calculator
When splitting actually helps
It depends on the half-life, not on preference. If the interval is short relative to the half-life, levels barely move between injections and splitting changes almost nothing. If the interval is long relative to the half-life, each dose largely clears before the next one lands, and splitting is the difference between a spike and a plateau.
Short esters gain the most. Testosterone propionate on a weekly schedule is a peak followed by several days of very little. The same weekly total every other day is a far steadier line. Cypionate and enanthate gain much less from going past twice weekly, which is why most TRT protocols stop there.
For GLP-1s the motive is usually tolerance, not smoothness. Semaglutide and tirzepatide already have half-lives near a week, so weekly dosing is fairly flat and splitting moves the curve very little.
More injections is a real cost. Every extra injection is another site, another entry into the vial and another chance to draw the wrong number. If the swing barely improves, the flatter curve is not worth it.
Splitting does not change your weekly exposure. The area under the curve is the same. If you are splitting in the hope of taking less, you are not; you are taking the same amount differently.
Common questions
How do I split a weekly dose into two injections?
Halve the per-injection amount and keep the weekly total the same. A 2.5 mg weekly dose becomes 1.25 mg twice a week, spaced evenly, so Monday and Thursday rather than two days running.
Does splitting a dose reduce side effects?
It lowers the peak, and where a side effect tracks the peak rather than the average, a lower peak can help. It does not reduce your weekly exposure at all.
Is splitting GLP-1 doses safe?
It is off-label. Manufacturer labelling for semaglutide and tirzepatide describes once-weekly dosing, and splitting is not a studied schedule. It is also mechanically riskier because each draw is smaller.
How do I know if splitting is worth it for my compound?
Compare the swing figures. If going from weekly to twice weekly barely moves it, the compound's half-life is already long relative to your interval and you are adding injections for very little.
Do I need to change my dose when I start splitting?
Not the weekly total. Splitting is a redistribution rather than a titration, and changing both at once leaves you unable to tell which change caused what.
Related tools
Half-life calculator
The full curve behind these numbers: build-up, steady state and washout.
TRT injection schedule
How often to inject by ester, with sample weekly schedules.
GLP-1 titration schedule
The manufacturer ladder, mapped from your start date.
Peptide dose calculator
Turn the new per-injection dose into units to draw.