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Bob's 27 Darts Calculator

Score Bob's 27, the doubles practice routine: start on 27, add each double you hit, lose it when you miss all three, and track your best score.

Level: Grades 2–3

  • Common Core standard 2.NBT.B.5Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
  • Common Core standard 3.NBT.A.2Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction.
Printable worksheet

Bob's 27 Darts Calculator

Inputs

One round per comma: the three darts (D1 S1 M; only that round's double scores) or just the number of hits, 0–3.

Result

Score so far

69

In progress: next target D11. Score 69, highest 69, 8 doubles hit in 10 rounds.

Game
In progress: next target D11
Highest score reached
69
Doubles hit
8
Doubles hit rate
26.7%
Best possible score
1,437

See the step-by-step solution ↓

Round by round
Round by round
RoundTargetHitsChangeScore
1D11+229
2D21+433
3D30−627
4D42+1643
5D50−1033
6D61+1245
7D70−1431
8D81+1647
9D90−1829
10D102+4069

Step-by-step solution

  1. A hit adds the double's value: in round 1, 1 hit on D1

    1×2=2

  2. Points won in the 6 rounds with at least one hit

    2+4+16+12+16+40=90

  3. Points lost: each round with no hits subtracts its double once (D3, D5, D7, D9)

    6+10+14+18=48

  4. Start on 27, add what was won and take off what was lost

    27+90−48=69

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Keep score for Bob's 27, a darts practice game for doubles, the shots that win legs. Former world champion Bob Anderson invented it. You start with 27 points and throw three darts at each double in turn, from double 1 up to the bull. Every double you hit adds its value to your score. But if all three darts at a double miss, you lose that double's value. Drop to zero or below and the game is over.

This calculator keeps the running score for you. Type each round's three darts, or just how many doubles you hit. It shows the score after every round and the highest score you reached. It also shows your doubles hit rate and when the game ended. The target changes every round, so the total is a fair measure of your doubles across the whole board. That makes it a good number to track from one practice session to the next.

Where it's used

Why this math matters outside the classroom:

  • Doubles practice. A player hitting double 7 twice adds 2 × 14 = 28 points, taking a score of 45 to 73.
  • Tracking progress. A club player logs a final Bob's 27 score after every session to see whether their doubles are improving.
  • Mental arithmetic. Players keep the running score in their head, such as 43 − 10 = 33 after missing every dart at double 5.
  • Coaching sessions. Coaches use the routine to show a player which part of the board's doubles costs them most points.

Grade level and standards: Grades 2–3; Common Core State Standards for Mathematics 2.NBT.B.5, 3.NBT.A.2. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Leave the bull round on to play the game as Bob Anderson described it. Or turn it off to stop after double 20.
  2. Type each round in order, separated by commas. Enter the three darts (D1 S1 M) or the number of doubles hit (0, 1, 2 or 3).
  3. Read your score, the game status and the round-by-round table.
  4. Want to finish all the doubles as practice, even after the game is lost? Turn on keep playing below zero.

What the inputs mean

Keep playing below zero (practice variant)
In the original game, reaching zero or less ends it. Many players carry on to the end anyway for the practice. With this on, every round counts and the score can go negative.
Rounds, D1 first
Round 1 is double 1, round 2 is double 2, and so on; round 21 is the bull. When you type darts, D means double, S single, T treble and M miss. Only the round's own double counts as a hit. In the bull round, only the bullseye (50, DB or BULL) counts. A single number from 0 to 3 is read as the number of hits.

Formula and method

start = 27
round N: hits × 2N added (bull round: hits × 50)
no hits in round N: 2N subtracted (bull round: 50)
game over when the score is 0 or less
best possible = 27 + 3 × (2 + 4 + … + 40) + 3 × 50 = 1437 (1287 without the bull)

N is the round number, which is also the number you aim at, and hits is how many of your three darts land in that double. Every round targets one double, and its value is twice the number (2N). One hit on double 7 adds 14, two hits add 28 and three add 42. If none of the three darts hits double 7, the round costs 14. The bull round is worth 50 per hit, and a missed bull round costs 50.

The score starts on 27, an odd number, and every change is even. So the score is always odd. It can never land on exactly zero, so in practice the game ends the moment the score goes negative. Missing the first few doubles completely (2 + 4 + 6 + 8 + 10 = 30) is enough to end the game in round 5. That's why the routine puts pressure on even the small doubles.

The highest score possible is three hits on every double: 27 plus 3 × 420 for doubles 1 to 20, plus 150 for the bull, which is 1437. Hit rate here is doubles hit divided by darts thrown, at three darts a round.

Worked example

An invented player, Marta Quillfeather, has played ten rounds. Rounds 1 to 5: D1 S1 M, M S2 D2, S3 M M, D4 D4 M, M M S5. Rounds 6 to 10: S6 D6 M, M M M, D8 S8 M, S9 M S9, D10 M D10.

  1. Round 1: one D1 hit adds 2, so 27 becomes 29. Round 2: one D2 hit adds 4, making 33.
  2. Round 3: no D3 hit, so subtract 6 for 27. Round 4: two D4 hits add 16 for 43. Round 5: no hit, subtract 10 for 33.
  3. Round 6 adds 12 (45), round 7 subtracts 14 (31), round 8 adds 16 (47) and round 9 subtracts 18 (29).
  4. Round 10: two D10 hits add 40, for 69. That is 8 doubles hit from 30 darts, a hit rate of 26.7%.

Result: After ten rounds Marta has 69 and is still in the game, with D11 next.

Understanding the result

A finished game's score is your benchmark. Bob Anderson said he regularly scored in the 600s and that his best was 811, which shows how hard the maximum of 1437 is. Compare your own totals over weeks rather than against anyone else's.

The highest score reached shows how well you started. If you often go out early, the small doubles are costing you. If you build a big total and then lose it, look at the doubles in the teens.

Assumptions and limitations

  • Three darts per round, at the doubles from 1 to 20 in order, then the bull.
  • Only the round's own double counts as a hit. A single or treble of the number, or a different double, is a miss.
  • The game ends at zero or below. Rounds typed after that are listed as not counted, unless you choose to play on.
  • One player and one game at a time.
  • Other versions, such as starting from double 20 or skipping the minus rule, aren't scored.
  • Rounds typed as hit counts can't be checked dart by dart.

Frequently asked questions

Who invented Bob's 27?

Bob Anderson, the 1988 world champion. He described it as a game he invented many years ago to keep doubles practice interesting, played from double 1 to the bull.

What is the highest possible score in Bob's 27?

1437, with all three darts hitting every double from 1 to 20 and the bull. Without the bull round, the maximum is 1287.

When does a game of Bob's 27 end?

When your score is zero or less, or after the last double. The score is always odd, so it never hits exactly zero. The game ends as soon as it goes negative.

Does a single or treble count in Bob's 27?

No. Only the double you are aiming at counts as a hit. A dart in the single 7 during the double 7 round is a miss.

Sources

How this calculator is checked

Method: Bob Anderson's own description in Dr. Darts' Newsletter issue 49 (June 2014): start on 27, three darts at each double from 1 to the bull, add each double hit, subtract the double when all three miss, game over at zero or less. Ending at D20 and playing on below zero are labelled options. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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