Why estimating beats testing for most lifters
A true 1RM attempt requires extensive warm-up, qualified spotters, and a willingness to absorb a heavy near-failure rep. For most recreational lifters, the marginal information you get from a true 1RM test isn’t worth the injury risk. A formula estimate from a 3–8 rep set is typically within ~5% of the true value and is repeatable week to week, which is what programming actually needs.
Where the formulas come from
The Epley formula was published in 1985 by strength coach Boyd Epley and is simple enough to do in your head. Brzycki’s 1993 paper proposed a hyperbolic model that performs slightly better at higher rep counts. Both are widely cited in NSCA and ACSM textbooks; neither is “the” right one — the differences between athletes (lever lengths, muscle fibre composition, neural drive) outweigh the differences between formulas.
What the result doesn’t tell you
1RM estimates assume good technique to failure on the rep set. If you stopped early, the estimate is conservative; if you cheated form, it’s optimistic. Estimates also don’t carry across exercises — your bench 1RM tells you nothing about your squat. Always retest after any layoff longer than two weeks before going heavy again.