- Theoretical best = best sector 1 + best sector 2 + best sector 3, from the valid laps of one session.
- Time available = your best lap minus your theoretical best. It is time you have already driven.
- Invalid laps set nothing. Untick Valid on any lap you were binned for.
The calculator
It opens with 7 laps from this site's worked example session. Lap 3 was the quickest of the night and was invalidated, so it is unticked and sets nothing. Replace the numbers with your own, or press Clear to start empty.
| Lap | Sector 1 | Sector 2 | Sector 3 | Lap time | Valid | Remove |
|---|---|---|---|---|---|---|
| 1 | 1:21.558 | |||||
| 2 | 1:21.210 | |||||
| 3 | 1:20.623 | |||||
| 4 | 1:20.960 | |||||
| 5 | 1:21.160 | |||||
| 6 | 1:21.194 | |||||
| 7 | 1:20.950 |
S1: your best lap was 0.147 s slower than lap 4 · S2: your best lap was 0.018 s slower than lap 5 · S3: your best lap was 0.118 s slower than lap 6
Purple marks the best of each sector and the best lap. With the example laps, the answer is 1:20.667 against a best lap of 1:20.950: 0.283 s already driven, in pieces.
How to work it out by hand
The calculator does four things, and you can do them on paper:
- List your laps with their sector timesWrite down every lap of one session with its three sector times. Keep it to one car, one track and one set of conditions — a lap on fresh softs and a lap on worn hards do not belong in the same sum.
- Leave out laps that should not countDrop the out-lap, the in-lap and any lap the game invalidated for track limits. An invalid lap sets no sector best, however quick it was.
- Take the quickest time in each sectorFor each sector, find the quickest time on any counted lap. These are your purple sectors, and they will usually come from different laps.
- Add the three togetherBest S1 + best S2 + best S3 is your theoretical best lap. Your best lap minus that is the time available: time you have already driven, just never in one lap.
Where to find your sector times
- In a game. Most racing games show sector splits on the timing screen or in a session's lap list. Copy them from there after a run.
- On track. Lap timers and timing apps that record splits give you the same three numbers per lap. If yours records more than three splits, add up all of the bests in the same way.
- From telemetry. If you record telemetry, you do not need to type anything: StintLab works out the theoretical best for every session of F1 25 and Assetto Corsa, along with an optimal lap cut into 100 m pieces.
Keep the number honest
A theoretical best is only useful if every piece of it could happen again. Three rules keep it that way:
- One session, one set of conditions. Mixing laps from a cold track and a hot one, or low fuel and high fuel, adds up sectors that were never driven together.
- Only valid laps. A sector driven by cutting the chicane is not a sector you own.
- Sectors must cover the lap. Each lap's three sectors should add up to its lap time. If they do not, a split is missing and the sum comes out too short.
What to do with the answer
Look at which sector holds the biggest gap between your best lap and your best sector. That is the third of the lap to work on first. To narrow it down to a corner, compare your best lap with the lap that set that sector — the lap comparison guide shows how to read the delta line that says where in the sector the time went.
The colours behind purple sectors, and why green is not the same thing, are in F1 sector times explained.
Questions
How do you calculate a theoretical best lap?
Take one session's valid laps, find the quickest first sector, the quickest second sector and the quickest third sector — usually from different laps — and add the three together. The calculator on this page does exactly that as you type.
What time formats can I type?
Seconds with up to three decimals, such as 28.512, or minutes and seconds, such as 1:02.250. A comma works as the decimal mark too. A box turns red if it cannot read what you typed.
Does an invalid lap count?
No. Untick a lap's Valid box and it sets no best sector and no best lap, which is also how StintLab treats a lap binned for track limits.
Is anything I type sent anywhere?
No. The sum runs in your browser; the times you type are not sent to StintLab or anyone else, and they are gone when you close the page.
Can I use it for real track days, or other games?
Yes. The arithmetic is the same for any car on any circuit split into three sectors: a sim, a karting session or a track day with a lap timer that records splits.
Why is my theoretical best so far from my best lap?
A big gap usually means your laps are inconsistent rather than slow: each sector has been driven quickly, just not on the same lap. That is the cheapest time to find, and consistency work is how you find it.