How the one rep max calculator works
How the formulas work
Epley (1985): weight × (1 + reps/30). Brzycki (1993): weight × 36/(37 − reps). Both derive a single-rep maximum from a submaximal set by modeling fatigue as a predictable decay — and they agree closely up to ~8 reps, diverging past 10–12 where fatigue stops being linear. The calculator averages them and shows each, because transparency beats false precision.
Why estimating beats testing
A true 1RM test taxes recovery for days and carries injury risk that scales with fatigue and ego. Estimating from a hard 5-rep set costs nothing and lands within a few percent. Test only when the training phase requires it (peaking blocks, competitions), estimate the rest of the year — the percentages barely move.
The reps-in-reserve calibration
Formulas assume true effort: the set ended when form broke or the bar stopped — not at a comfortable 4 reps of a possible 8. Calibrate with RIR (reps in reserve): a set at 2 RIR is roughly a 2-rep-boosted estimate. Lifters who consistently end sets early will under-estimate their max, which is a feature when it keeps loading honest.