Quick answer: 20 kg is achievable for most people carrying it, but it takes roughly six to ten months at a sustainable pace — not the one to two months the search results promise. Done at that speed with enough protein and resistance training, it stays off. Done in six weeks, most of it returns within a year.
The timeline, honestly
At 0.5 kg a week, 20 kg takes about 40 weeks. At 0.75 kg a week, closer to 27. Starting from a higher weight makes the early months faster, so a realistic shape is 3–4 kg in month one, settling to 2–2.5 kg a month after that.
That is nine months of sustained effort. It is worth saying plainly, because the main reason people fail at 20 kg is not the difficulty — it is being told it takes six weeks, missing that, and concluding it is impossible.
Why the last 5 kg behaves differently
As you get lighter, you burn less at rest simply because there is less of you, and your body adapts to the deficit. The same eating pattern that produced 3 kg a month at the start produces 1.5 kg a month later. This is expected, not a plateau to break through by eating less again.
The usual adjustments are to recalculate maintenance at your new weight, hold protein up, and accept a slower rate rather than a deeper cut.
What makes 20 kg stay off
Muscle. It is the one variable that separates people who lose 20 kg and keep it from people who lose it twice. Protein at 1.2–1.6 g per kg and resistance training two or three times a week is what preserves it through a long deficit — and preserved muscle is what keeps your maintenance calories high enough to live at afterwards.
The maintenance phase deserves as much planning as the loss phase, and almost nobody gives it any.
Where medical treatment fits
For a 20 kg goal, many people are in the BMI range where medically supervised treatment is appropriate, and GLP-1 trials have shown mean body-weight reductions in the 15–21% range over 68–72 weeks — which for a 100 kg person is 15–21 kg. That is the same order as this goal, achieved on a comparable timeline, with the deficit made easier to sustain rather than shortcut.
It is not a substitute for the protein and the training. Medication changes how hard the deficit is to hold; it does not change what protects muscle while you hold it.
Starting well
Get baseline bloods — thyroid, HbA1c, lipids, vitamin D, ferritin. If something there is contributing, you want to know in month one rather than month six. Then set a nine-month expectation, track the weekly trend, and stop weighing your progress against a ten-day promise nobody has ever kept.
