How to Set Swim Send-Off Intervals

What does “10 x 100 on 1:40” actually ask you to do? It means you leave the wall every 100 seconds, ten times in a row. Whatever part of that time you do not spend swimming becomes your rest. Once you see a send-off as swim time plus rest, you can build any set to fit your speed and your goal.

What Is a Swim Send-Off?

A send-off is the fixed clock time between the start of one repeat and the start of the next. It includes both your swim and your rest. On a 1:30 send-off, you push off exactly 90 seconds after your last push-off.

The same number gives different rest to different swimmers. U.S. Masters Swimming explains it with a 50 on 1:30. A swimmer who finishes in 45 seconds rests 45 seconds, while one who needs 1:20 rests only 10.

Send-Off Versus Rest Interval

Coaches write sets two ways. A send-off fixes the leave time, so faster swimming earns more rest. A rest interval fixes the pause instead, such as “10 seconds rest,” and you leave 10 seconds after each touch no matter your speed.

Read the notation from left to right. “10 x 100 on 1:40” means ten repeats of 100, leaving every 1:40. “10 x 100 with :15 rest” means ten repeats with a 15-second pause after each one.

The Send-Off Formula

The core rule is short: send-off equals swim time plus planned rest. Convert both to seconds, add them, and turn the total back into minutes and seconds. A 1:25 swim is 85 seconds, so adding 15 seconds of rest gives 100 seconds, or 1:40.

Next, round to a number the clock makes easy. Send-offs are usually rounded to a clean 5 or 10 seconds. A 1:22 swim plus 15 seconds is 1:37, which rounds up to 1:40 and gives 18 seconds of rest.

Total set time uses one more rule. Multiply the send-off by one less than the number of reps, then add the final swim. The last rest does not count, because the set ends when you touch.

Your swim time comes from a steady effort you can hold across the set. Our guide on how to calculate swimming pace per 100 shows how to find that number from any timed swim.

Building 10 x 100 on 1:40, Step by Step

Take a swimmer who holds 1:25 per 100 and wants about 15 seconds of rest. Four steps turn those two numbers into a full set plan.

Step one is the send-off. 85 seconds plus 15 seconds is 100 seconds, so the set reads 10 x 100 on 1:40. That number already sits on a clean 5-second mark.

Step two is the leave times. A pace clock sweeps 60 seconds, so a 1:40 send-off lands at :00, :40 and :20 before returning to :00. The pattern repeats every three reps, or every 5 minutes.

Step three is the total time. Nine full send-offs take 900 seconds, and the tenth swim adds 85 more. That is 985 seconds, or 16:25 for the whole set.

Step four is a check. Counting the final rest by mistake gives 16:40, which overstates the set by 15 seconds. Across four sets in a workout, that error grows to a full minute.

How Much Rest Does Each Training Goal Need?

Longer rest suits faster, harder swimming, and shorter rest suits steady aerobic work. The sets below come from published swim studies and coaching guides, not from a single universal rule.

Now turn rest into send-offs. The swimmer who holds 1:25 per 100 takes 1:35 for the race-pace set, with 10 seconds of rest. For sprints, a 50 swum in 30 seconds with 2 minutes of rest gives a 2:30 send-off.

That sprint set matches the 1:4 work-to-rest ratio the sprint study used. The long pause lets you swim each 50 near full speed. Short rest does the opposite, keeping effort steady and fatigue building across the set.

Threshold sets sit between these extremes. Our guide to critical swim speed and threshold pace covers the test that sets the swim time for those repeats.

Slip-Ups That Cost You Rest

Most broken sets come from clock habits rather than fitness. These five errors show up in lanes at every level.

• Using a best time as the swim time. A send-off built on one fast 100 leaves almost no rest by rep four. Build it from a pace you can repeat.
• Mixing yards and meters. A 100 yard swim is only 91.44 meters. A 1:25 yard swimmer needs about 1:33 per 100 meters before any rest.
• Reading the wrong hand. Many pace clocks show a minute hand and a second hand. Watch the second hand and note only its position.
• Adding the last rest to the total. The set ends at the final touch, so 10 x 100 on 1:40 runs 16:25, not 16:40.
• Leaving early to catch a better mark. Pushing off 3 seconds early on every rep steals 27 seconds of rest across ten reps.

When Should You Change Your Send-Offs?

Change a send-off when your rest drifts far from the plan for several sets in a row. Too much rest means you got faster, and almost none means the send-off is too tight.

Watch the rest you actually get on the final reps. A set planned for 15 seconds that ends with 20 seconds of rest calls for a send-off 5 seconds faster next time. A set that ends with 5 seconds calls for 5 seconds more.

Adjust in steps of 5 seconds, one set at a time. Retest your pace every few weeks, since the whole system depends on an honest swim time.

Change the distance and the send-off scales with it. A 200 swum in 3:05 with 25 seconds of rest goes on 3:30, and five of them take 17:05. Run any new set through the send-off and total set time calculator before you print your workout.

Common Questions About Swim Send-Offs

References

This guide covers the arithmetic of send-offs and total set time, with rest examples drawn from published swim sets. Match rest to your own fitness and your coach’s plan. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.