Forty Thieves Solitaire: the game where we could not find the ceiling

Forty Thieves is a two-deck patience with a fierce reputation. You start with forty cards face up in ten columns, a 64-card stock you go through only once, and a rule that lets you move just one card at a time. Every column must be built down in suit.

On this site we usually lead with the ceiling: how many deals are winnable with perfect play. For Forty Thieves we could not measure it, and we found no published figure either. What we have is a floor. A computer player that does not know the order of the stock, and never undoes a move, won 5.8% of 3,000 deals. That player is weak, so read 5.8% as "at least this many," not as how winnable the game is.

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Forty Thieves by the numbers

Why a floor, and why it is low

A ceiling needs a solver that can search the whole game. Forty Thieves has 104 cards, a long stock, one-card moves and ten columns, and we did not run a solver on it. Instead we used a program that plays like a careful but short-sighted person: it looks a limited number of moves ahead, does not know which card the stock will give it next, and never takes a move back.

That kind of player is at a real disadvantage in Forty Thieves. With only one pass through the stock and in-suit building, a single poor choice early on can decide the game. A person using Undo to test lines will do better. So treat 5.8% as a starting point, not a verdict.

For context, the site solitairex.io groups Forty Thieves with its "expert" games, which it lists at 11% or less. It does not say how that range was measured, so we mention it only as a rough comparison.

The rules as this site plays them

Forty cards in ten columns

Two decks, 104 cards. Ten columns of four cards, all face up, which uses 40 cards. The other 64 form the stock.

One card, one suit

• Build down in the same suit: the 9 of hearts goes only on a 10 of hearts.
• Only one card moves at a time.
• Any card can go into an empty column.

A single pass of 64 cards

• Turn one card at a time onto the waste. Its top card is playable.
• There is no redeal. One pass through the stock is all you get.

A finished game

All 104 cards on the eight foundations, two per suit, each built up from Ace to King.

Playing above the floor

Empty a column as early as you can

With single-card moves, an empty column is how you unpack a buried card. Any card can go there, so it is worth a lot.

Take the free Aces

In 57.3% of deals at least one Ace is playable from the opening layout. Send it home, then look for the other copy of that suit, since there are two of every card.

Think before every stock card

You see each stock card once. Before turning the next one, make sure you have used everything the waste and tableau allow.

Do not bury low cards

Placing a card on a column can trap an Ace or 2 underneath for a long time. With one-card moves, digging it out is slow.

Do what the program cannot: undo

Our program never undoes a move, which is one reason its win rate is so low. You can. Try a line, and back out if it goes nowhere.

Reading a Forty Thieves layout in the first minute

Because all forty starting cards are face up, you can size up a deal before you move. Three things are worth checking.

• Where the Aces are. An Ace at the bottom of a column can go straight home. An Ace buried under three cards needs those three moved first, one at a time, each onto a card of its own suit.
• Which columns are closest to empty. Every column starts with four cards. Look for the one whose cards can all find a home quickly. Emptying it gives you the space you need for everything else.
• Same-suit pairs already in order. A 7 of clubs sitting on the 8 of clubs is progress you did not have to make. Protect those pairs.

Once play starts, the stock is where most choices happen. Each card comes once, so before you turn it over, ask whether anything on the waste or the tableau is still playable. A card left on the waste can still be played later, but only after you use every card that lands on top of it.

Finally, remember there are two of every card. If one 5 of hearts is stuck, the second one may turn up in the stock. Leaving a spot open for it can pay off.

Inside the test, one step at a time

The solitaire-online.us team tested Forty Thieves in September 2026.

1. Reading the rules from our game code. Two decks, ten columns of four face up, a 64-card stock with no redeal, in-suit building, one card at a time and any card into a space.
2. Rebuilding the game. We wrote Forty Thieves as a Python program with those rules.
3. Dealing the cards. 3,000 deals, each from a numbered seed.
4. Choosing the player. A look-ahead program that searches up to 300 positions per turn over the cards it can see, without knowing the stock order. It only turns a new stock card once no tableau or waste move helps.
5. Running it. Every deal played to a finish, won or stuck.
6. Checking against published research. We found no published winnability figure for Forty Thieves.
7. Working out the margin of error. A 95% range means the true value would fall inside it in 19 of 20 repeats. Wins: 5.0–6.7%.
8. What the numbers cannot tell you. The ceiling. Our program is weak for this game, so its win rate says little about how many deals are winnable.

The code behind the floor

The study is written in Python 3.11, standard library only. Forty Thieves has its own module, fortythieves.py, built from the same program we used for Diplomat, and a shared runner spreads the deals across processor cores with Python's multiprocessing.

The program scores each position it can reach: points for every card on a foundation and every empty column, and penalties for cards sitting on lower cards. It then picks the move that leads to the best score. The 95% ranges come from the Wilson score method.

Claude (Anthropic's AI assistant) helped us build and check the program and sketch this page. It did not supply any figures. All the figures above are outputs of the program itself.

By Admin, solitaire-online.us (Solitairen OOD). Study date: September 19, 2026.

Ceiling questions from players

How many Forty Thieves games can be won?

We do not know yet, and we found no published answer. Our weak program won 5.8%, so the true figure is at least that.

Why is it so hard?

One pass through the stock, one card at a time and in-suit building leave little room for mistakes.

Can several cards be moved together?

No. Only one card at a time.

Is an empty column restricted to Kings?

No. Any card can go into an empty column, which makes them very valuable.

What is a gentler two-deck game?

Try Solitaire Double or Diplomat Solitaire. For a one-deck game with every card visible, try FreeCell.