A "one rep max" from a submaximal set is always an estimate — but which formula you use changes the number, and most calculators only show you one.
Epley formula calculator, the more common default
Lift 100 kg for 5 reps, and the Epley formula estimates a 116.7 kg one-rep max — a simple linear formula that's the most commonly used default across strength calculators.
Brzycki formula calculator, a different curve entirely
The same 100 kg × 5 reps input gives 112.5 kg under the Brzycki formula — a 4.2 kg gap from Epley, using a different mathematical curve. The two formulas diverge further as rep count climbs, especially above 10 reps.
Training percentage calculator, using the estimate for programming
Rather than picking one formula and treating it as fact, this calculator shows both plus a training percentage table (60-95% of the Epley estimate) — useful for programming your next sets without needing a separate max-effort attempt every time.
