Calculators for coaches
The numbers behind the training and the coaching business, worked out with the formula in plain sight.
Each calculator ships the formula explained, a table of precomputed values and the assumptions it runs on, so you can check the result or do the arithmetic by hand. Two answer the load: estimated 1RM and the percentage of 1RM for each RIR. The third answers the business: what to charge per session.
3 calculators
How much to charge per session
The formula
Price per session = (Target income + Fixed costs) ÷ (Sessions per month × (1 − Deductions))
The price you need to charge per session comes from dividing what you want to earn plus your fixed costs by the sessions you bill each month, adjusted for what tax and payment fees take. With a target of 2,000 a month, 300 in fixed costs, 60 sessions and 25% in deductions, the price is 51 per session. Fewer sessions raise the price in the same proportion.
What is your estimated 1RM?
The formula
Epley: 1RM = weight × (1 + reps / 30). Brzycki: 1RM = weight × 36 / (37 − reps). The two agree almost exactly at 10 reps and diverge from there: Epley returns the higher number on long sets, and Brzycki becomes unstable near 37 reps, where its divisor approaches zero.
Your estimated 1RM is the heaviest load you could lift once, calculated from a set you actually did instead of measured directly. With the Epley formula, 1RM = weight × (1 + reps / 30): 100 kg for 5 reps estimates 117 kg. It is an estimate, not a measurement, and it loses accuracy as reps climb. Under 10 reps it is dependable; past 12 treat it as a reference rather than a number.
What percentage of 1RM does your RIR correspond to?
The formula
Equivalent reps = reps performed + RIR. That total is how many reps you could have done to failure, and it is what you read off the %1RM table. Using Epley inverted: %1RM = 1 / (1 + equivalent reps / 30). A set of 5 with 2 RIR is 7 equivalent reps, so 1 / (1 + 7/30) = 81%.
RIR is the reps you have left in the tank when the set ends. Converting it to a percentage of 1RM needs both numbers: how many reps you did and how many you left. A set of 5 with 2 RIR means you could have done 7, and that lands around 81% of 1RM. The short rule: add reps and RIR together, then read that total off the percentage table. Each extra RIR drops the load by roughly 3 to 4 percentage points.
