A pacer has to run the target pace for the whole race while talking, signalling, checking the watch, handing out drinks and watching the group. That only works if the target pace feels comfortable to you. The pacing buffer measures how much room you have between your own ability and the pace you are asked to hold.
The buffer formula#
We compare two finish times for the same distance: the target time of the pace group and your verified personal best (PB). Both are converted to seconds.
Buffer B = (target time − PB) ÷ target time × 100
The result is a percentage: how much faster than the target you have proven you can run.
Worked example#
You have a marathon PB of 3:25:00 and want to pace the 4:00 group.
| Step | Working | Result |
|---|---|---|
| Target time in seconds | 4 × 3,600 | 14,400 s |
| PB in seconds | 3 × 3,600 + 25 × 60 | 12,300 s |
| Difference | 14,400 − 12,300 | 2,100 s |
| Buffer | 2,100 ÷ 14,400 × 100 | 14.6% |
A 14.6% buffer means you are running well within yourself. Compare a runner with a 3:50 PB applying for the same group: (14,400 − 13,800) ÷ 14,400 = 4.2%. That runner would be close to their limit for four hours. On a hot day, after a bad night's sleep or with a small injury, they could fail, and their group with them.
The thresholds#
The CDPP course and the applicant scoring system use the same thresholds:
| Buffer (B) | Rating | Buffer score |
|---|---|---|
| Below 7% | Unsafe | 0 points |
| 7% to 10% | Acceptable but tight | 50 + (B − 7) × 10 |
| 10% to 20% | Ideal safety window | 80 + (B − 10) × 2 |
| Above 20% | Large reserve | 100 points |
- Minimum: 7%. Below this, you should not pace that group.
- Target: 10–20%. This is the comfortable window where you can focus fully on your runners.
For the worked example above: 80 + (14.6 − 10) × 2 = 89.2 points. A 3:40 PB for the 4:00 group gives a buffer of 8.3% and a score of 50 + 1.3 × 10 = 63 points: allowed, but tight.
The event's own requirements#
The Pacer Support Guide sets buffers by pace group, from about 8% for faster, more ambitious groups (such as a 3:45 marathon or 1:45 half marathon) to about 13% for slower, more relaxed groups (such as a 5:00 marathon or 2:30 half marathon). See who can be a pacer for the full tables.
These figures are the event's minimum requirement for each group. The 7% in this course is an absolute floor that never changes. Always meet whichever is higher. If the event asks 13% for the 5:00 group, 7% is not enough.
Why slower groups need more#
Slower groups are usually paced by recreational runners, and races in tropical climates get hotter as the morning goes on, so slower groups spend more time in the heat. A larger buffer gives a pacer room to absorb heat, fatigue and the extra work of helping runners at water stations. See heat and humidity.
Use a recent PB, ideally from the last 12–18 months, on a similar course. A PB from five years ago says little about your fitness today.
Key takeaways#
- Buffer B = (target time − PB) ÷ target time × 100, with both times in seconds.
- Never pace with a buffer below 7%; aim for 10–20%.
- A 3:25 PB pacing the 4:00 marathon group gives a 14.6% buffer.
- The event's own buffer per pace group (about 8–13%) is a minimum; meet whichever requirement is higher.
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