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How to Plan Splits for a Target Swim Time
Manesh Jayawardhana
CIO & Co-founder
Twenty-four minutes for 1500 metres is 1:36 per hundred. Knowing that is the easy part.
Swimming it is a question of how those ninety-six seconds are distributed across fifteen hundreds, and the distribution changes the total more than most swimmers expect.
Going out too fast costs more than it gains
The most common way a target swim is missed is a fast first quarter.
Swimming above your sustainable pace early accumulates fatigue disproportionately. The time gained in the first 300 metres is small; the time lost across the remaining 1200 is much larger, and the second half degrades progressively rather than settling at a slightly slower pace.
The physiological picture is that effort above a sustainable threshold produces fatigue that does not clear while you continue swimming. You cannot recover mid-race the way the plan assumes.
That asymmetry is why conservative early pacing produces faster totals than aggressive early pacing, even though it feels slower at the time.
Even, negative or controlled positive
Even splitting — the same pace throughout. Theoretically the most efficient distribution and demanding to execute, because it feels too easy early and very hard late.
Negative splitting — second half faster than the first. Slightly less efficient in theory and more reliable in practice, because it builds in a margin against going out too fast. Most distance swimmers who hit their targets are negative splitting by a small amount.
Controlled positive — first half deliberately faster, accepting a slower finish. Sometimes correct in a race where position matters, and generally slower on the clock.
| Strategy | First half | Reliability |
|---|---|---|
| Even | Target pace | Efficient, hard to execute |
| Negative | Slightly slower | Most reliable |
| Positive | Faster | Fast start, slow finish |
For a 24:00 target on a negative split plan, the first 750 goes out around 1:37.5 per hundred and the second comes back at 1:34.5.
Pool length changes everything
A time in a 25 m pool is not comparable to a time in a 50 m pool.
The short course has twice as many turns, and a push-off is faster than swimming. A well-executed turn and underwater phase gains time on every wall, so short course times are typically quicker for the same effort.
That has two consequences. Comparing a personal best across pool lengths without adjusting is comparing different things. And a swimmer with weak turns loses much of the short course advantage, which is a training signal rather than a pacing one.
Open water removes walls entirely and adds current, sighting and drafting. Clock splits become far less useful there, and pacing by effort and stroke rate is more reliable.
Practise the pace, not just the distance
A split plan is only useful if you can feel the pace it asks for.
Swimming repeats at target pace — a set of 100s on a fixed send-off at exactly the split you plan to hold — teaches the body what that speed feels like. Without it, race pace is a number on paper and the actual first hundred is whatever adrenaline produces.
The useful set is one where the pace is held across the whole set rather than started fast. A set of ten 100s where the first is quick and the last three are slow is training exactly the pattern you are trying to avoid.
Descending sets, where each repeat is slightly faster, train the negative split directly.
Common mistakes to avoid
- Going out at target pace in the first hundred, which is faster than target effort.
- Comparing short course and long course times directly.
- Planning splits never swum in training.
- Ignoring turns as a source of time in short course.
- Using clock splits in open water, where conditions dominate.
How to do it with Swim Split Time Predictor
The Swim Split Time Predictor builds the split plan.
- Enter the distance and target time.
- Choose a strategy — negative splitting is the most reliable for distance events.
- Read the per-hundred splits and note the first-half target specifically.
- Swim the plan in training before racing it.
Other training tools are in the tools directory.
Frequently asked questions
Is a negative split better?
For most swimmers it is more reliable. Going out too fast produces a disproportionate slowdown later, so a slightly conservative first half usually gives a faster total than an even effort started too hard.
Does pool length change the plan?
It changes the times. A 25 m pool has twice as many turns and push-offs are faster than swimming, so short course times are typically quicker for the same effort.
What about open water?
Splits are far less reliable — no walls, plus current, sighting and drafting. Pace by effort and stroke rate rather than by the clock.
Final thought
Swim the first half slower than feels right. Every distance swimmer who misses a target time went out faster than the plan, and none of them noticed at the time.