A lot of lifters use rep-based max estimates, then get confused when two formulas give slightly different results from the same set. That is not a sign that one of them is broken. It simply means different formulas make different assumptions about how reps relate to max strength. That is why many lifters compare methods on OneRepMaxCalculators.com before settling on the one that feels most useful.
Why formulas do not all agree
A one-rep max formula is an estimate, not a direct measurement. It is trying to predict your likely max from a set you already completed.
Where the difference comes from
As reps climb, endurance starts affecting performance more. Some formulas react more strongly to that change than others, which is why estimates can drift apart.
Lower reps usually behave more consistently
If you estimate from a clean set of 3 to 5 reps, many formulas will stay closer together. Once you start estimating from 8, 10, or more reps, the gap can grow.
Why this matters in training
A bigger difference between formulas means you need to be more careful about which number you actually use for programming.
Epley vs Brzycki in plain language
These are two of the most common formulas because they are practical and easy to compare.
What lifters should focus on
The goal is not to find the formula that gives the biggest number. It is to find the one that creates working weights that actually feel realistic in the gym.
The best formula is often the one you use consistently
If you change methods all the time, your training numbers become harder to compare. A consistent method makes progress easier to track and programming easier to trust.
Final takeaway
1RM formulas change with reps because rep performance is not a perfect mirror of true max strength. That is normal. The most useful approach is to understand the difference, choose one method that fits your training, and use it consistently enough that the estimates become practical.
