[CALCULATOR]
What that set says you could lift once.
[WHAT THIS DOES]
An estimated one-rep max converts a set of submaximal reps into the single-rep load it implies, so sets at different weights and rep counts become comparable across a training block. Base uses the Epley formula and only trusts it to about twelve reps, because the estimate degrades badly above that.
The formula
e1RM = weight * (1 + reps / 30)This is Epley. There are a dozen alternatives — Brzycki, Lombardi, O'Conner — and they agree closely at low rep counts and diverge at high ones. Epley is used here because it is the one Base uses internally, and because agreement between your own sessions matters more than agreement with any particular published equation.
Reps in reserve belong in the input
A set of five at 225 with two reps left is a very different data point from a set of five at 225 taken to failure, and a formula fed only "225 for 5" cannot tell them apart. This calculator adds your RIR to the rep count before estimating, which is what makes two sets at different efforts comparable.
That is also the argument for recording RIR at all. Without it, double progression cannot distinguish twelve reps at 0 RIR — a genuine ceiling that earns a load increase — from twelve reps at 4 RIR, where the load was simply too light and should jump immediately. A rep-only log will slow-walk you through weights you could already handle.
Where it stops working
Above roughly twelve effective reps, every 1RM formula degrades, and it degrades in a direction: high-rep sets over-predict maximum strength, because a set of twenty is limited by local muscular endurance and buffering capacity rather than by peak force production. Base refuses to compute an e1RM above twelve reps rather than showing a number it does not believe.
The other limit is technical. An e1RM assumes your form at one rep resembles your form at eight. For a deadlift that is roughly true; for a barbell row it is often not, and a squat that turns into a good morning at maximal load has an e1RM that describes a lift you cannot actually perform.
What it is genuinely good for
Not for quoting. For trending. Across a training block your working sets will vary in weight and reps for reasons that have nothing to do with strength — a deload, a bad night, a change in exercise order. Plotting e1RM converts all of them onto one axis, and the slope of that line is the honest answer to whether the block is working.
Base uses that slope as one of the four inputs to its deload decision: an e1RM trend below about 0.1% per week across your main lifts counts as a stall, and a stall alongside a second fatigue signal is what triggers the recommendation.
What to do next
Log RIR on every working set for four weeks, then look at the e1RM trend rather than at any single session. The line is the information.
Questions
How accurate is a one-rep max calculator?
Within a few percent for sets of one to five reps, degrading steadily above that and unreliable past about twelve. High-rep sets over-predict maximal strength, because a set of twenty is limited by local endurance rather than peak force. Use it as a trend line across a block, not as a number to attempt.
Which 1RM formula is best?
They agree closely at low rep counts and diverge at high ones, so consistency matters more than choice. Epley is used here because it is what the app uses internally, and comparing your own sessions to each other is the only comparison that matters.
Should I include reps in reserve?
Yes. A set of five with two reps left and a set of five taken to failure are different data points, and a formula fed only the completed reps cannot distinguish them. Adding RIR to the rep count before estimating is what makes sets at different efforts comparable.
Does e1RM drop when I add endurance training?
It can, briefly, and that is usually fatigue rather than lost strength. A sustained flat or falling e1RM trend across several weeks alongside a second fatigue signal is the point at which it means something — that is exactly the pattern that should trigger a deload.