Fatigue Percent of 1rm Calculator
Track your fatigue percent 1rm with our free sports calculator. Get personalized stats, rankings, and performance comparisons.
Reviewed by Sher, Sports Science & Nutrition Specialist
Formula
Fatigue % = ((True 1RM - Estimated 1RM) / True 1RM) x 100
Where True 1RM is your tested one-rep maximum, and Estimated 1RM is calculated from a fatigued set using the Epley formula: Weight x (1 + Reps / 30). The difference reveals how much fatigue has accumulated. RPE adjustment adds (10 - RPE) x 2.5 to account for subjective effort levels.
Worked Examples
Example 1: Squat Session Fatigue Assessment
Problem:A lifter with a 300 lb squat 1RM performs a set of 8 reps at 225 lbs with an RPE of 8. What is their fatigue percentage?
Solution:Percent of 1RM = 225 / 300 = 75%\nEpley Estimated 1RM = 225 x (1 + 8/30) = 225 x 1.267 = 285 lbs\nFatigue % = (300 - 285) / 300 = 5.0%\nRPE Adjustment = (10 - 8) x 2.5 = 5.0%\nAdjusted Fatigue = 5.0% + 5.0% = 10.0%
Result:Working at 75% of 1RM with 10.0% adjusted fatigue. Reps in reserve: 2.
Example 2: Bench Press Fatigue After Multiple Sets
Problem:A lifter has a 200 lb bench press 1RM. After 4 sets, they manage 6 reps at 155 lbs at RPE 9. What is the accumulated fatigue?
Solution:Percent of 1RM = 155 / 200 = 77.5%\nEpley Estimated 1RM = 155 x (1 + 6/30) = 155 x 1.20 = 186 lbs\nFatigue % = (200 - 186) / 200 = 7.0%\nRPE Adjustment = (10 - 9) x 2.5 = 2.5%\nAdjusted Fatigue = 7.0% + 2.5% = 9.5%
Result:Working at 77.5% of 1RM with 9.5% adjusted fatigue. Only 1 rep in reserve.
Frequently Asked Questions
What is fatigue percent of 1RM and why does it matter for training?
Fatigue percent of 1RM measures how much your maximal strength capacity has temporarily decreased during a training session relative to your true one-rep maximum. When you perform multiple sets and reps, accumulated fatigue reduces the weight you can lift compared to a fresh state. Tracking this metric helps you understand how much fatigue your training is generating, which is critical for managing recovery and avoiding overtraining. A fatigue percentage between 5-15% is typical for most strength training sessions. Values above 20% indicate significant accumulated fatigue that may require extended recovery periods or deload weeks to manage properly.
How is the Epley formula used to estimate fatigue levels?
The Epley formula estimates your one-rep maximum based on the weight lifted and the number of repetitions completed, using the equation: Estimated 1RM = Weight x (1 + Reps / 30). By comparing this estimated 1RM from a fatigued set to your known fresh 1RM, you can calculate the fatigue percentage. For example, if your fresh 1RM is 300 pounds but after several sets your estimated 1RM drops to 270 pounds, that represents a 10% fatigue accumulation. The Epley formula works best for rep ranges between 1 and 10 repetitions and becomes less accurate at higher rep ranges where cardiovascular and muscular endurance factors become more dominant than pure strength.
What is RPE and how does it relate to fatigue measurement?
RPE stands for Rate of Perceived Exertion, typically measured on a scale from 1 to 10 in strength training, where 10 represents a maximum effort with zero reps in reserve. An RPE of 8 means you could have performed approximately 2 more repetitions before reaching failure. RPE directly correlates with fatigue because as fatigue accumulates, the same weight feels heavier and RPE increases. By incorporating RPE into fatigue calculations, you get a more personalized and accurate picture of your actual fatigue state. This subjective measure complements objective load-based calculations because it accounts for factors like sleep quality, nutrition, and psychological stress that pure numbers cannot capture.
How should I adjust my training weights based on fatigue percentage?
When your fatigue percentage exceeds 10-15%, consider reducing your working weight by 5-10% for subsequent sets to maintain movement quality and reduce injury risk. For strength-focused training, keep fatigue below 10% by using longer rest periods of 3-5 minutes between sets. For hypertrophy training, moderate fatigue of 10-20% is acceptable and may even be beneficial for muscle growth stimulus. If your calculated fatigue consistently exceeds 20% within a single session, you may be performing too much volume or using loads that are too close to your maximum. Periodically testing your actual 1RM every 4-8 weeks ensures your fatigue calculations remain accurate as you get stronger.
References
Reviewed by Sher, Sports Science & Nutrition Specialist · Editorial policy