FortiorStrength
How to calculate your one-rep max without testing it
Your one-rep max (1RM) is the heaviest weight you could lift for one good rep. You do not have to test it to see roughly where it sits. Fortior estimates it from the weight, the reps and the reps in reserve of the sets you already log.
Why estimate instead of testing
A true max test is tiring, takes planning, and can only be done once in a while. An estimated 1RM lets you follow your strength using ordinary working sets, so the number can update every time you train. It also gives different rep ranges a common yardstick: a set of 5 and a set of 8 can both be expressed as "about this much for one rep".
How to calculate an estimated one-rep max
You need three things from a hard set: the weight, the reps you completed, and how many more good reps you could have done. That last number is your reps in reserve (RIR).
- Work out reps to failure. Add the reps you did to your reps in reserve. Five reps with two left means you could have done seven.
- Put the weight and reps to failure through a formula. Several well-known formulas turn them into an estimated max. They disagree with each other, so Fortior runs five of them.
- Average the five. The mean is the estimate for that set.
A worked example
A lifter does 5 reps at 100 kg (220 lb) and judges that they had 2 reps left. Reps to failure is 5 + 2 = 7.
| Formula | Estimated 1RM |
|---|---|
| Epley | 123.3 kg |
| Brzycki | 120.0 kg |
| Lombardi | 121.5 kg |
| O'Conner | 117.5 kg |
| Lander | 121.1 kg |
| Average | 120.7 kg (about 266 lb) |
The same 5 reps at 100 kg give a different answer depending on how hard the lifter rates the set:
| Reps in reserve | Reps to failure | Estimated 1RM |
|---|---|---|
| 0 (nothing left) | 5 | 114.6 kg |
| 1 | 6 | 117.6 kg |
| 2 | 7 | 120.7 kg |
| 4 | 9 | 127.0 kg |
In this example each extra rep in reserve adds about 3 kg to the estimate. An honest effort rating matters as much as the weight on the bar.
Which sets Fortior uses
The formulas lose accuracy as the rep count climbs, so Fortior uses them only when reps to failure is between 1 and 11. A set of 8 reps with 3 in reserve (11) counts. A set of 10 reps with 2 in reserve (12) is outside the range. A few views convert longer sets another way, and a set that long cannot set an estimated-max record.
- Only completed working sets count. Warm-up sets do not.
- Each variation is tracked on its own. A chin-up and a wide-grip pull-up have separate estimates.
- One point per training day. On a lift's Strength page, each day's point comes from that day's strongest set.
What a blank reps in reserve counts as
Zero means you reached failure. A blank field means you did not track effort, and Fortior never treats it as failure. Where the math needs a number, a blank counts as 2 reps in reserve, and the set is marked as not recorded. So 100 kg for 5 reps with the field left blank is estimated at 120.7 kg, the same as the 2-in-reserve row above.
Verified top sets and how Fortior learns your formula mix
Fortior starts with all five formulas weighted equally. A set of 1 to 3 reps taken to failure (reps in reserve 0) is a verified top set, the most direct evidence of what you can lift. When one is logged, Fortior compares each formula's prediction with the weight you actually lifted and shifts weight toward the formulas that came closest. This is learned separately for each exercise, and it updates once, when you finish the workout. A blank reps in reserve can never be a verified top set.
The learned mix shapes the trend on that lift's Strength page. Personal-record checks and highlights always use the equal-weight average, so a record is judged the same way every time. See personal records and highlights.
Why an estimate is not a tested max
- It depends on your rating. The table above shows a spread of about 12 kg for the same set. If you rate every set as easier than it was, the estimate rises with no change in strength.
- The formulas are general curves, not fitted to you. Even one rep at 100 kg taken to failure gets estimates from 100 to 103.3 kg across the five formulas, and the average is 101.4 kg.
- Setup and bodyweight matter. How bodyweight counts, your setup, technique and range of motion all change what a set shows. For push-ups and pull-ups, see bodyweight strength.
- Use it for the trend. An estimate is best for seeing whether your strength is moving up or down. It is not a promise of what you would lift on a max attempt.
In the app: open Progress, choose Strength, and select an exercise. You will see its current estimated 1RM, the change over the range you pick, your best, and the top set behind each session. Basic strength trends are free; deeper strength analytics are part of Fortior Premium.
Strength estimates are educational and based on your own logs. They are estimates, not tested maxes, and Fortior is not medical advice.