One-Rep Max Calculator

Research shows the Epley formula is most accurate for low rep ranges (1-5 reps), while Brzycki performs better for moderate reps (6-10). A validation study found Epley predicted 1RM within 2.7kg from 3RM tests. For 10 reps, both formulas return identical results. The NSCA recommends using multiple formulas and comparing results, as individual variation in muscle fiber composition affects accuracy.

Above 10 reps, muscular endurance and cardiovascular factors increasingly influence performance, confounding pure strength measurement. Research in the Journal of Strength and Conditioning Research shows prediction error increases from 2-5% (under 10 reps) to 10%+ (above 15 reps). High-rep sets introduce fatigue variables that skew results. For reliable estimates, test with weights you can lift for 1-10 reps with good form.

Direct 1RM testing is recommended when peaking for competition, establishing true maxes for experienced lifters, or when estimates diverge significantly from performance. However, the NSCA advises submaximal testing (3-5RM) for novice lifters, injury-prone individuals, and during regular training phases. 1RM tests require 48-72 hours recovery and can suppress strength for 3-5 days afterward.

Accumulated fatigue significantly impacts both actual 1RM performance and prediction accuracy. NSCA research confirms that 1RM "is not stable in novice populations and can be suppressed by fatigue from previous training." Testing after inadequate recovery produces artificially low results. For accurate estimates, test after 2-3 rest days, use standardized warm-up protocols, and limit attempts to 5 per session with full recovery between sets.

Formula accuracy varies by exercise. Research shows bench press estimates are most reliable due to the movement's stability. Squat and deadlift involve more technical variables and fatigue factors that introduce error. The Brzycki formula validation found consistent accuracy for bench press but slight variations for compound lower-body lifts. For deadlifts, grip fatigue can limit rep performance before muscular failure, potentially underestimating true 1RM.

The NSCA recommends using estimated 1RM as a baseline, then applying conservative training percentages. Rather than training at 100% of estimated max, use 85-90% as your working maximum (training max concept). This accounts for daily variation, estimation error, and accumulated fatigue. Re-test or recalculate every 4-6 weeks to track progression.