Roughly 0.5 to 1% of body weight per week. At 100 kg that is 0.5 to 1 kg a week. Sustained loss above about 1% is the pattern most associated with a larger share of lean tissue in what comes off.
That is a guideline for composition, not a rule about safety, and it is not a reason to change a dose on your own.
What the trials actually produced
In STEP-1, participants on semaglutide 2.4 mg lost an average of 14.9% of body weight over 68 weeks. Spread across that period, that is well under 0.5% a week on average.
In SURMOUNT-1, tirzepatide produced 15.0% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg over 72 weeks. Again, large totals over a long time rather than fast weekly loss.
Both trials describe the same shape: loss beginning within the first few weeks, continuing steadily, and flattening late — in STEP-1 the average stopped falling around week 60. You can see what those figures mean at your own starting weight with the weight loss calculator.
The practical point is that the headline numbers people quote came from a slow, sustained process, not a rapid one.
Why faster is not better
Rate of loss is one of the clearest inputs into how much of the loss is lean tissue. The larger the deficit, the less energy is available for maintaining muscle, and the more of it the body is willing to give up.
There is a second problem. Very rapid loss on these medications usually means very low total intake, which means protein intake is low too — so the two factors that most protect lean mass are both compromised at once.
Getting to the same destination more slowly generally arrives with more muscle intact.
The early weeks are an exception
Do not judge the first two or three weeks by this standard. Early loss includes a substantial amount of water — glycogen stores fall when intake drops, and each gram of glycogen carries several grams of water with it.
That produces a fast start that is not fat loss and not muscle loss. It also produces the discouraging second phase when the rate drops to something normal, which people frequently misread as the medication stopping working.
If you are consistently above 1%
Three or more weeks running above that threshold is worth acting on. In order:
- Check your protein against your target. Fast loss with low protein is the worst combination and it is the most common one.
- Make sure resistance training is happening. Two sessions a week.
- Consider eating a little more. This is counterintuitive on a weight-loss medication and it is often the correct move.
- Raise it with your prescriber if it continues. Dose changes and titration pauses are clinical decisions. Do not make them because of an article or a calculator, including ours.
If you are below 0.5%
That is usually fine, and often better than fine. Slower loss is more protective of lean mass, and total loss over a year is what matters rather than any given week.
If the scale has stopped entirely for several weeks, that is a different question — see why weight loss stalls.
Knowing where you actually are
Our muscle check uses rate of loss as one of three inputs and will tell you whether yours is the thing costing you most. It calculates the rate from your own numbers, which is more reliable than a weekly impression — scale noise makes any single week a poor guide.