Darts checkouts from 2 to 40

Even numbers: one dart at the double

A double is worth twice its number, so every even score from 2 to 40 is a one-dart finish: 2 is D1, 20 is D10, 36 is D18 and 40 is D20, called tops. Halve the score and you have your target. You get three darts at it in a visit, and the double is the only way out, because under double out the last dart must be a double or the Bull.

Why odd numbers cannot go out with one dart

Every double is an even number, and so is the Bull (50). An odd score can never be finished by a double alone, so it needs a single first: throw the single that leaves a double, then go for the double. On 37 that is 5 to leave 32, then D16.

Odd numbers: which single to throw

The chart throws the single that leaves the best double it can reach, in this order: 32 (D16), 40 (D20), 36 (D18), 24 (D12), then 16 (D8), 8 (D4) and the rest. Below 40 that makes a simple pattern, and the single is always 1, 3, 5 or 7:

Why not take the biggest single? On 39, a 19 leaves 20 (D10), which works, but miss that into the single 10 and you are on 10 (D5), and one more miss leaves 5, odd again. A 7 leaves 32, which halves all the way down.

With one dart left in a visit and an odd score, you cannot finish, so throw the single that sets up the next visit. Set Darts in hand to 1 in the checkout calculator and it names the single for any score.

The D16 halving chain

32 is the favourite leave in darts because a miss into the single leaves another double, and so does the next miss, all the way down to D1:

1. 32: D16. A single 16 leaves 16.
2. 16: D8. A single 8 leaves 8.
3. 8: D4. A single 4 leaves 4.
4. 4: D2. A single 2 leaves 2.
5. 2: D1. A single 1 leaves 1, a bust, so the chain ends here.

32 is the highest double in the ring that keeps halving to another double until D1: 32, 16, 8, 4, 2. Compare D20, which goes 40, 20, 10 and then 5, or D18, which goes 36, 18 and then 9. That is why the chart prefers to leave 32, and why it plays 50 as 18, D16 rather than straight at the Bull.

Every checkout from 2 to 40

The finish the app suggests for every score in the band. For an even score, the last column shows where you are if the double lands in the single; for an odd score, which double the single leaves.

Busts at the end of a leg

Low scores are where busts happen. Score more than you need, leave 1, or reach 0 without a double, and the visit is a bust: the score returns to what it was before the visit and the turn passes. On 2, a single 1 leaves 1: bust. On 10, a single 10 reaches 0 without a double: bust. On 16, any dart worth more than 16 goes below zero: bust. Here is the end of a leg from 101 with two busts: