Between 1.2 and 1.6 grams per kilogram of body weight per day, aiming for the middle of that range, and towards the upper end from about age 60. At 90 kg that is roughly 110 to 145 g a day.
You can get your own number from the protein calculator, which also shows what it looks like in actual food.
Why not the 0.8 figure on the packet
The widely quoted 0.8 g per kg is a population-level minimum for healthy adults who are not losing weight. It is designed to prevent deficiency, not to preserve muscle, and it assumes energy intake is adequate.
Neither of those assumptions holds while you are in a deficit. When the body is short of energy it breaks down more protein for fuel, so the same intake goes less far. The requirement goes up precisely when appetite — and therefore intake — is going down.
That is the whole reason this question matters more on a GLP-1 than off one. The medication does not change your protein requirement. It changes how easy it is to meet it.
Where the range comes from
It is not a single study. It is the number several independent clinical nutrition groups landed on when they looked at protein and muscle preservation, and the consistency across them is the reason to trust it more than any one paper.
The PROT-AGE group and the ESPEN expert group both put the requirement for older adults well above the standard recommendation, and higher still for those who are ill or in a deficit. The weight-loss literature summarised by Cava and colleagues points the same way: higher protein plus resistance training is the combination that reliably changes the composition of the weight lost.
We use 1.4 g per kg as the middle target and step it to 1.5 from age 60. Every constant is published on the site rather than hidden.
The upper end, and when to stop
There is no benefit demonstrated to going far above this range for muscle preservation, and at some point extra protein simply displaces other food you also need. The 1.6 figure is a sensible ceiling for this purpose, not a wall.
One genuine exception. If you have kidney disease and a clinician has given you a protein target, theirs governs and this page does not apply to you. Higher protein intake is not appropriate for everyone, and no calculator can see your bloods.
Spreading it across the day
Total daily intake is what matters most, and it matters considerably more than distribution. But distribution is not nothing, and on these medications it is unusually practical advice.
Appetite suppression is typically strongest in the day or two after an injection and later in the day generally. Front-loading — getting 30 to 40 g at breakfast — takes the largest share of the target while eating is easiest. Aiming at roughly a quarter of your target at each of four eating occasions is a reasonable default, and three larger ones is fine if that fits your day better.
If you are nowhere near it
Most people who have not counted are further off than they expect, and the gap is usually invisible because nothing feels different. Count for three days once, honestly, and compare it against your number. That single exercise is worth more than any amount of reading, and it is the input that most narrows the estimate in our muscle check.
If the gap is large, do not try to close it in a week. Add one protein-dense item to the meal where appetite is best and let that settle before adding another.