Double start means you have to hit a double to open a leg as well as to close it. Until a dart lands in the doubles ring or the bullseye, nothing you throw counts. Every dart before that scores zero, but it still goes on your dart count and still drags your average down.
In professional darts it is used at exactly one televised tournament: the PDC World Grand Prix, which in 2026 runs from 28 September to 4 October at the Mattioli Arena in Leicester. Everywhere else the pros play straight-in, double-out. Below is how the rule works, what it costs you in darts and in average, and the piece of arithmetic that decides whether a nine-darter is even possible.
How double in, double out works
The game is still 501. What changes is the opening.
- Your first scoring dart must land in a double. Any of the twenty doubles on the outer ring will do, and the bullseye counts too.
- The opening double does score. Hit double 20 and you take 40 off, leaving 461. It is not a free pass into the leg, it is your first 40 points.
- Darts thrown before you open score nothing. Your total stays on 501 and the visit is wasted, but the darts are still counted.
- The finish is unchanged. You still have to land the last dart in a double, or the bull, to take the leg out exactly.
The Professional Darts Corporation sets this out plainly in its own rules: some versions of 501 require a double start, where a player must begin on a double as well as check out on one, and the World Grand Prix is the event that uses it. The PDC describes the tournament as requiring players to “begin and finish every leg on a double or the bullseye”.
Does the bullseye count as a double?
Yes. The inner bull scores 50, which is twice the 25 of the outer ring, so it is treated as a double at both ends of the leg. You can open a leg on the bull and you can finish one on it.
The outer bull is different. It scores 25, it is a single, and it will not open or close a leg. If you are unsure which ring is which, our guide to the dartboard number order and how the board is divided up walks through singles, trebles, doubles and the two bull rings.
What happens if you miss the double
Nothing. Your score stays on 501 and the throw passes to your opponent. Both players can burn through several visits without getting started, and in a double-start match that is normal rather than embarrassing. Legs that would be over in fifteen darts routinely stretch past twenty.
The only tournament that uses it: the World Grand Prix
The World Grand Prix has been played double-in, double-out since the very first staging in 1998, at the Casino Rooms in Rochester, which Phil Taylor won. It is the only televised PDC major that uses the rule, and the format is the event’s whole identity.
| 2026 World Grand Prix | Detail |
|---|---|
| Dates | 28 September – 4 October 2026 |
| Venue | Mattioli Arena, Leicester |
| Field | 32 players — the top 16 on the PDC rankings, plus the top 16 on the ProTour Rankings not already qualified |
| Format | Sets, each set the best of five legs. Best of 3 sets in round one, best of 5 in round two and the quarter-finals, best of 9 in the semi-finals, best of 11 in the final |
| Prize fund | £750,000 in total, with £150,000 to the winner |
| Defending champion | Luke Littler, who beat Luke Humphries 6–1 in the 2025 final |
Phil Taylor has won it eleven times and Michael van Gerwen six. Only those two have ever successfully defended the title, which is what Littler is attempting in Leicester.
Away from the professional game the rule turns up far more often than people expect. Plenty of pub leagues and club competitions play double-in over 301 or 501, usually because it makes short games less of a lottery.
What the double start actually costs you
This is the part no one puts a number on, so we have. The maths is simple enough to be worth doing properly.
If your chance of hitting your chosen double with any given dart is d, then the expected number of darts you spend getting into the leg is 1 ÷ d. The chance of failing to open at all in your first three-dart visit is (1 − d)³, and the chance of still not being away after two full visits is (1 − d)⁶.
| Chance of hitting the double, per dart | Darts spent opening, on average | Chance of not opening in your first visit | Chance of still not opening after two visits |
|---|---|---|---|
| 10% | 10.0 | 72.9% | 53.1% |
| 15% | 6.7 | 61.4% | 37.7% |
| 20% | 5.0 | 51.2% | 26.2% |
| 25% | 4.0 | 42.2% | 17.8% |
| 30% | 3.3 | 34.3% | 11.8% |
| 35% | 2.9 | 27.5% | 7.5% |
| 40% | 2.5 | 21.6% | 4.7% |
Read the middle of that table and you have the explanation for everything that looks strange about a Grand Prix leg. A club player who hits one double in five needs five darts to get going, and will fail to open in his first visit more often than not. Even at 40% per dart, which is a serious standard, you are still spending two and a half darts a leg before your score moves at all, and you will draw a blank in your opening visit better than one time in five.
These are modelled figures, not measured ones. They show what a given level of doubling accuracy implies, not what any named player actually throws.
Why double-start averages look so low
A three-dart average is simply the points scored divided by the darts thrown, multiplied by three. In a completed leg of 501 that gives you 1,503 divided by the number of darts. The wasted opening darts sit in the denominator and score nothing, so they hit the average hard.
| Extra darts spent opening | Total darts in the leg | Three-dart average | Drop |
|---|---|---|---|
| 0 (straight-in) | 15 | 100.20 | — |
| 1 | 16 | 93.94 | −6.26 |
| 2 | 17 | 88.41 | −11.79 |
| 3 | 18 | 83.50 | −16.70 |
| 4 | 19 | 79.11 | −21.09 |
| 6 | 21 | 71.57 | −28.63 |
One wasted visit — three darts — turns a hundred average into an eighty-three average without the player scoring one point worse than usual. That is the single most useful thing to understand about watching the Grand Prix: an 88 average there is not a bad performance, and comparing it with a 100 average from a straight-in event is comparing two different measurements.
There is a second, smaller cost people miss. Your opening dart goes into double 20 for 40 rather than treble 20 for 60, so you give up twenty points of scoring on top of the darts you waste.
Can you hit a nine-darter starting on a double?
Yes, and it has been done three times at the World Grand Prix. Brendan Dolan got there first, in his 2011 semi-final against James Wade, earning the nickname The History Maker. His three visits were 160, 180 and a 161 finish of treble 20, treble 17, bullseye. Three years later James Wade and Robert Thornton both hit one in the same second-round match.
What is rarely explained is how narrow the window is. We worked through every legal route, and the answer is stark.
There are 21 doubles on a dartboard, counting the bull. Only three of them can open a nine-darter. After your opening double you have eight darts left: seven that can score a maximum of 60 each, and a last one that must be a double worth at most 50. That caps what those eight darts can clear at 470, so any opening double worth less than 31 is mathematically dead before you throw a second dart. Doubles 16, 18 and 19 clear that first hurdle but fail the next one, because no combination of seven scoring darts plus a double lands on their exact remainder. That leaves three.
| Opening double | Left to clear in 8 darts | Doubles you can finish on |
|---|---|---|
| Double 17 (34) | 467 | Bullseye only |
| Double 20 (40) | 461 | Bullseye only |
| Bullseye (50) | 451 | Double 17, double 20 or the bullseye |
| Any other double | 463 or more | None — no legal nine-dart route exists |
So unless you open on the bull, the only way a double-start nine-darter can end is on the bullseye. Dolan finished on the bull, and he had no other option. For comparison, a straight-in 501 nine-darter can finish on any of six different doubles: 12, 15, 17, 18, 20 or the bull.
Route analysis calculated by ArrowHeadz by exhaustive search of every legal combination of nine darts from 501 under double-in, double-out, and checked a second time by hand.
Which double should you start on?
There is no rule about it, so this is judgement rather than fact, but the arithmetic narrows it down more than you would think.
Double 20 is the sensible default for most players. It is worth 40, the highest of the twenty outer doubles. It sits at the top of the board, in the same place your eye and your arm have been working all match if you score on the 20s. And it is one of only three doubles that keeps a nine-darter alive, which matters less for your Tuesday night league but tells you something about how much scoring room it leaves.
The bull pays 50 and opens the widest set of finishing routes, but it is a far smaller target, and spending two extra darts to gain ten points is a poor trade for almost everyone.
The argument against double 20 is a practical one we hear in the shop all the time: plenty of players are simply better at a double they have practised for years, usually double 16 or double 8 because of how those numbers halve down. If you hit double 16 at twice the rate you hit double 20, the table further up this page settles the argument for you. Ten points of opening score is nothing next to two saved darts.
How to practise the double start
The double start rewards one specific skill, and it is not scoring. It is being able to put the first dart of a visit into a thin outer ring cold, with no rhythm built up.
- Play double-in 501 against yourself. Count the darts you spend opening across twenty legs and divide. That number is your real d from the table above, and it is usually lower than people expect.
- Open on a different double every leg. Round the board from double 1 upwards. It stops you leaning on one comfortable target and shows you which doubles you genuinely cannot hit.
- Throw your first dart of the session at a double. The hardest dart in a double-start leg is always the first one, so practise it cold rather than after a warm-up.
None of this works if the board or the throwing line is wrong, so it is worth checking the official height and oche distance before you start counting anything. If you are practising doubles seriously you will wear out the outer ring first, which is the one part of a board that shows its age quickest — worth bearing in mind when you look at the bristle dartboard range. Our accuracy guide covers the grouping work that sits underneath all of it.
One equipment note, offered as opinion rather than fact: double-start play flatters a dart you can group tightly with over a dart you can score heavily with. If you have a set that feels precise but slightly light on scoring power, this is the format where it comes into its own. Our guide to choosing a dart weight is the place to start if you are weighing that up.
Frequently Asked Questions
Which darts tournament is double start?
The PDC World Grand Prix, and only the World Grand Prix among televised PDC majors. It has used double-in, double-out since it began in 1998. The 2026 edition runs from 28 September to 4 October at the Mattioli Arena in Leicester.
Can you start on the bullseye in a double-in game?
Yes. The inner bullseye scores 50, which is the double of the 25 outer ring, so it opens a leg exactly as any other double does. The outer bull scores 25, counts as a single, and will not start you off.
Do you have to start on a double in normal darts?
No. Standard 501 is straight-in, double-out: you can score with your first dart and only the finishing dart has to be a double. Double start is the exception rather than the rule, used at the World Grand Prix and in some league and pub formats.
Can you get a nine-darter starting on a double?
Yes, and three have been thrown at the World Grand Prix: Brendan Dolan in 2011, then James Wade and Robert Thornton in the same 2014 match. Only three opening doubles make it arithmetically possible — double 17, double 20 and the bullseye — and unless you open on the bull, the bullseye is the only double you can finish on.
Why are averages lower at the World Grand Prix?
Because the darts thrown at the opening double score nothing but still count. A leg that would take fifteen darts straight-in takes eighteen if you waste one visit getting started, and that alone drops the three-dart average from 100.20 to 83.50 without the player scoring any worse.
What is the hardest double to hit in darts?
Every double is physically the same size, so the difficulty is in what a miss leaves you rather than in the target. Double 1 is the one most players name: land inside it and you are left needing 1, which cannot be finished, so the visit is dead. Double 20 and double 16 are the most practised and therefore the ones most players hit most often.
What happens if you go past zero in double-in, double-out?
The same as in any 501 game. If you score more than you need, finish on anything other than a double, or leave yourself on 1, the visit is void and your score goes back to what it was at the start of the throw. The double-start rule only changes how a leg begins, not how a bust works.
Sources: PDC Rules of Darts; PDC World Grand Prix tournament information; PDC schedule of play for the 2026 World Grand Prix. Prize fund breakdown, round formats and nine-dart records cross-checked against published tournament records and Sky Sports coverage. All probability, average and nine-dart route calculations on this page were worked out by ArrowHeadz and verified by two independent methods.
