520 lb works out to 5x45 + 1x10 + 1x5 per side plus the bar — call it 525 lb in practice, since gyms rarely stock the odd change. 2 reps sits at the reliable end of the range these formulas were fitted on, so the 43 lb spread here is about as tight as the method gets. Your 495 lb set represents about 95% of the estimated max.
Why 2 reps gives a tight estimate
A double is the shortest set these seven equations accept, and it is where they agree most closely. Every one of them was regressed on sets of two to ten reps, so two sits at the near edge of the fitted band rather than outside it, and the 43 lb between 509 and 552 lb is about as narrow as this method ever gets. The uncertainty at two reps is not in the arithmetic, it is in the set: a double you could have taken one rep further looks identical on paper to one that genuinely stopped you.
Training loads from a 520 lb max
Programmes are written as percentages of the max, not as absolute weights. From 520 lb, rounded to the nearest 5 lb:
| Percentage | Load | Typical set |
|---|---|---|
| 95% | 495 lb | Heavy single |
| 90% | 470 lb | Doubles and triples |
| 85% | 440 lb | Sets of four to five |
| 80% | 415 lb | Sets of six |
| 75% | 390 lb | Sets of eight |
| 70% | 365 lb | Volume work, ten or more |
520 lb is 5x45 + 1x10 + 1x5 per side plus the bar, 525 lb loaded. At this load the 43 lb the formulas disagree by is bigger than a pair of 10s, which is a good argument for programming off the lower estimate — 509 lb — and letting the bar prove you wrong rather than the other way round. Warm-up jumps also get long here; work up in percentages rather than in fixed plate increments.
The formulas behind this answer, and their limitations
The table above the fold is Epley (1985), Brzycki (1993), Lombardi (1989), O'Conner (1989), Wathan (1994), Lander (1985) and Mayhew (1992), each applied to 495 lb for 2 reps; the headline figure is their median. All seven assume a set taken close to failure with clean technique. At 2 reps you are inside the band they were fitted on, so the largest error here is not the equation but judging how close your set really was to failure — three reps left in the tank reads exactly the same to them. They also under-rate strong, experienced lifters, who hold a higher percentage of max at any rep count than the regression average. The full account — the populations behind each equation, what a bounced rep does to it, and why we stop at ten reps — is set out on the methodology page. Warm up thoroughly and use safety bars or a spotter before going anywhere near 520 lb. This is a training estimate, not medical advice.