How fast should I be losing? Rate of loss by week from the published curves

The trials publish endpoints and figures, not weekly tables. So any week-by-week number is either read off a graph or interpolated. This page is honest about which is which.

Measured anchors

These are the numbers actually reported in the papers, all mean percent change from baseline on brand product at label doses with diet and activity counselling.

Note what the two intermediate anchors imply. On semaglutide, roughly 70 percent of the 68-week loss had happened by week 20. On tirzepatide, the week-36 SURMOUNT-4 figure equals the week-72 SURMOUNT-1 figure at 15 mg, in a different population that had escalated to the top doses. The middle of therapy is where the curve is steep.

An interpolated table

Between the anchors, the plateau checker uses a first-order model: cumulative change at week t equals the endpoint times (1 - e^(-kt)) / (1 - e^(-kT)), with k = 0.04 per week and T the trial's final week. The constant was chosen so that about 60 percent of the total is reached by week 20, which matches the shape of the published figures. The table below is that model. The last row of each column is measured; nothing else is.

Two things to notice. First, the model's week-20 semaglutide value (-8.8 percent) undershoots the STEP 4 measured -10.6 percent, which tells you the real early curve is somewhat steeper than the model and the late curve somewhat flatter. Second, the per-week rate in the last third is less than a tenth of the rate in the first month. A rate of a quarter of a percent a week at month nine is on the curve, not off it.

Turning percent into your units

Percent is the unit the trials use because it makes a 90 kg person and a 130 kg person comparable. To convert: a 100 kg (220 lb) start at -0.5 percent per week is 0.5 kg (1.1 lb) per week. At -0.1 percent per week it is 100 g (0.2 lb), which no bathroom scale resolves week to week. That is the arithmetic reason to weigh weekly and average, covered in how to weigh yourself.

The spread inside the average

STEP 1 reports how many people crossed each threshold at week 68: 86.4 percent lost at least 5 percent, 69.1 percent at least 10, 50.5 percent at least 15, and 32.0 percent at least 20 (PubMed 33567185). SURMOUNT-1 at 15 mg: 91 percent lost at least 5 percent and 57 percent at least 20 (PubMed 35658024). Read those from the other direction. One in seven people on semaglutide lost under 5 percent. Half lost under 15. A rate below the table is where a large minority of trial participants lived, on the brand product, at the label dose, with monthly counselling visits.

Compounded products, slower titrations, missed doses and a different starting weight or metabolic history all move an individual off these curves in either direction. The curves are a reference frame, not a forecast. If the reference frame is what you want in numbers, the FormBlends Calculators site applies the same arm means to a starting weight.