You squatted 100 kg for 5 and NOYU says your estimated 1RM is 117 kg. You have never had 117 kg on your back and you might not want to. The number is still useful, and knowing where it comes from tells you how far to trust it.
What a one-rep max is for
Your one-repetition maximum is the heaviest weight you can lift once with good form. Coaches use it as a reference point: a programme might ask for sets at 80% of your max, and progress on a lift is easiest to see as a change in that one number.
Testing it directly is a poor way to find it. A true max attempt is fatiguing, needs a spotter and carries the highest injury risk of anything you do in a gym. Most people should not test it often, and many should not test it at all.
Estimating it from a normal set
The alternative is to estimate it from a set you were going to do anyway. NOYU uses the Epley formula, published in 1985 and still one of the most widely used: take the weight, multiply by one plus the repetitions divided by 30.
So 100 kg for 5 is 100 multiplied by 1.17, or about 117 kg. Do 100 kg for 8 next month and the estimate rises to 127 kg. You never touched a heavier bar, but you demonstrated more strength, and the estimate captures that.
NOYU takes the strongest working set from each session and plots one estimate per session, so the chart on an exercise page is the trend of your best set over time. Warm-ups are left out, because a warm-up is not a strength expression.
Why it stops at 12 reps
The formula assumes each extra repetition costs about the same fraction of your max. That holds well for heavy sets of one to five, reasonably for sets up to about ten, and then falls apart. A set of 15 or 20 is limited by muscular endurance and how much discomfort you tolerate, not by how strong you are, and two people with the same max can differ by five or more reps at a light weight.
NOYU draws the line at 12. A working set of 13 or more repetitions produces no estimate and cannot set an estimated 1RM record. Above that line the number would be a guess dressed as a measurement, and we would rather show nothing.
How much to trust it
Treat the estimate as accurate to within a few kilograms when it comes from a heavy set, and as a rough guide when it comes from a set of ten. It is best at one job: showing whether you are getting stronger on a lift over weeks and months, using sets you were doing anyway.
It is not a licence to load 117 kg tomorrow. Estimated strength and demonstrated strength are different things, and the gap between them is where injuries happen. If you want to know your true max, work up to it deliberately over several sessions, with a spotter, on a day your Readiness is good.
