Ultra Pace Calculator

The math we're doing

Three things slow ultrarunners down: distance fade (your pace gets worse the longer you go), elevation gain (Naismith), and your specific ultra fitness (a marathoner with no long-run base will fade harder than someone with three 50-milers in the legs).

We start from your recent marathon time and convert it to a flat-mile pace. Then we apply a distance-fade exponent — your pace gets worse as a power function of distance. The Riegel formula uses an exponent of 1.06; for ultras with a real ultra-fit base, we use 1.07–1.10 depending on your fitness selection.

Then we add a Naismith-style climb penalty: 12 minutes per 1,000 feet of vert (the realistic version, not the strict version). The result is a finish-time estimate that's usually within 8% of what people actually run on race day.

How to read your output

• Estimated finish time — the realistic version, including expected fade and climb. If your goal is faster than this, train for it.
• Average pace — what every mile would average to. You won't run this evenly; first half will be faster, last quarter will be the slowest.
• Vert per mile — see the Vert Calculator article for what this means in context.
• Slowdown vs marathon — your average pace at the ultra distance compared to the marathon you started from. Expect 25–60% slowdown depending on distance and vert.

Calibrating against your last race

The fitness selector is the dial that matters most. If you've finished an ultra before, set "Solid" or "Strong" and compare the calculator's output to your actual finish. If it's within 5%, the calculator is calibrated for you — use it for the next race. If you finished significantly faster, you're a Strong climber; if you blew up and dropped, you're a First-timer regardless of mileage.