Estimating a one-rep max honestly

A single estimated maximum is the most quoted number in a gym and the least examined. It comes from one of five formulas, each fitted to a different group doing a different lift, and they disagree by an amount that grows with every rep. The disagreement is the useful part.

Why there are five formulas

Epley, Brzycki, Lombardi, O'Conner and Wathan were each derived from a particular study population and a particular exercise. None is right; each is a line through somebody else's data. At three reps they land within about two per cent of each other, which means the estimate is trustworthy to a kilo or two. At ten they can be five per cent apart — several kilos — and past twelve they are largely measuring how long you can keep going, which is a related but different quality.

Reps in reserve changes the question

Every one of these formulas assumes the set ended because another rep was not happening. A set of five with three left in the tank is, for this purpose, closer to a set of eight, and treating it as a five will over-estimate your maximum substantially. Being honest about what you left behind matters more to the accuracy than which formula you pick.

Track the estimate, not the weight on the bar

Sessions are not comparable by weight alone. Three at 100 kg is a better performance than five at 95, which is better than three at 95. The estimated maximum puts them all on one axis, which is the only way to see a trend through a block where the rep ranges change. Watch the slope over months — day to day, sleep, food and stress move a top set by more than a fortnight of training does.

Load what the gym can actually make

A programme that prescribes 87.3 kg is prescribing something impossible. Work out what the plates in front of you can make, round down, and note what you gave up. With pairs down to 1.25 kg the smallest change you can make is 2.5 kg, which is a 2.5% jump on a 100 kg lift — worth knowing when a programme asks for a 2% increase.

Frequently asked questions

Should I test a true one-rep max?

Rarely. It carries the most injury risk of anything you can do in a gym, it needs experience and ideally a spotter, and it tells you roughly what a hard set of three already tells you. Most training decisions only need an estimate that is consistent with itself over time.

Which formula is best?

There is no best. Brzycki tends to read lower at high reps and Epley higher; the median of several is more robust than any one. What matters is using the same approach consistently, so that changes over time mean something.

My estimate went down. Am I weaker?

Probably not. A single session is affected by sleep, food, stress and how long since the last hard session, far more than by a fortnight of training. One low session is noise; a downward slope over six weeks is information.