Critical Swim Speed Calculator
Divide the difference between two times by the difference in distance and you get the speed at the threshold where lactate starts to build. The gap between 400 m and 200 m is the time for the extra 200 m, so half of it is the pace per 100 m.
Your numbers
Per 100 m
102.5s
Finish time
1,538s
Formula
Per 100 m = (400 m time − 200 m time) ÷ 2
Swim both trials all-out on the same day with full recovery between. Cruising the 200 m makes the result look slower than your real threshold.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| 400 m time (s)An all-out 400 m time. | 380 | 0 and up |
| 200 m time (s)An all-out 200 m time from the same day. | 175 | 0 and up |
Step by step
Quick reference table
Results when only 400 m time (s) changes and everything else stays put.
| 400 m time (s) | Per 100 m (s) | Finish time (s) |
|---|---|---|
| 190 | 7.5 | 113 |
| 285 | 55 | 825 |
| 380 | 102.5 | 1,538 |
| 570 | 197.5 | 2,963 |
| 760 | 292.5 | 4,388 |
What each result means
| Result | At default values |
|---|---|
| Per 100 m (s)Time to cover 100 m — the swimmer’s pace unit. | 102.5 |
| Finish time (s)Your finish time if the pace holds all the way. | 1,538 |
Common mistakes
Swim both trials all-out on the same day with full recovery between. Cruising the 200 m makes the result look slower than your real threshold.
Glossary
- 400 m time
- An all-out 400 m time.
- 200 m time
- An all-out 200 m time from the same day.
- Per 100 m
- Time to cover 100 m — the swimmer’s pace unit.
- Finish time
- Your finish time if the pace holds all the way.
Frequently asked questions
Q. How is Critical Swim Speed Calculator calculated?
Per 100 m = (400 m time − 200 m time) ÷ 2 — Divide the difference between two times by the difference in distance and you get the speed at the threshold where lactate starts to build. The gap between 400 m and 200 m is the time for the extra 200 m, so half of it is the pace per 100 m.
Q. Can you walk through an example?
With 400 m time 380s, 200 m time 175s, the answer is Per 100 m 102.5s.
Q. What do I need to enter?
Enter 400 m time, 200 m time. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only 400 m time (s) moves the answer to 400 m time (s) 190 → Per 100 m (s) 7.5 and 400 m time (s) 760 → Per 100 m (s) 292.5. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Swim both trials all-out on the same day with full recovery between. Cruising the 200 m makes the result look slower than your real threshold.
Related calculators
These calculators help you understand health figures; they do not replace diagnosis or prescription. See a clinician if you have symptoms.