Swim Threshold Pace Calculator

About this calculator

Threshold pace in swimming (closely related to Critical Swim Speed, or CSS) marks the sustainable effort level right at the boundary where lactate production and clearance are roughly balanced — swim faster than this and lactate accumulates rapidly, swim at or below it and the pace can, in principle, be held for a long time. Coaches estimate it from a test set, typically a 400m and 200m (or similar paired) time trial: the difference in time divided by the difference in distance gives the pace per 100m that represents your threshold, without needing a lab lactate test.

Once known, threshold pace becomes the anchor for structuring an entire training week: interval sets are prescribed as a percentage faster or slower than threshold (e.g., "8×100m at threshold minus 2 seconds" for VO2max work, or "16×100m at threshold plus 5 seconds" for aerobic endurance), so swimmers and coaches use it constantly to calibrate main-set intensity and to track fitness gains over a season as the threshold pace gets faster.

This calculator converts your test-set distance and time into your threshold pace per 100m and your corresponding speed, giving you the anchor number your interval training can be built around.