Forty Thieves Solitaire: the two-deck game that asks for patience

Forty Thieves has a reputation, and it's earned. You get two full decks, forty cards on the table in ten neat columns, and a big stock of 64 cards you can go through only once. Cards move one at a time, and they only build in their own suit. It's a wonderful game if you like a challenge, and a frustrating one if you play it on autopilot.

We measured that directly. A computer player that looks a little way ahead but doesn't know what's coming in the stock, and never takes a move back, won just 5.8% of 3,000 deals. That's a floor, and a low one: a thoughtful person using Undo will do better. But it's a clear signal. Forty Thieves rewards careful play much more than casual play.

What a casual player is up against

For another view, solitairex.io groups Forty Thieves with four-suit Spider in its hardest tier, with win rates of 11% or less. It doesn't say how that range was worked out (source). Both figures point the same way: this is one of the toughest games on the site.

A word of caution about our 5.8%: this program is not very strong, so it's a floor, not "how winnable Forty Thieves is." We didn't run a solver that sees every card for this game, so we don't know how many deals could be won with perfect play.

Forty Thieves rules on this site

• Two decks, 104 cards. Forty are dealt face up into ten columns of four. The other 64 form the stock.
• The stock turns over one card at a time onto a waste pile. There's no redeal: one trip through, and that's it.
• Building: down one rank in the same suit. A 9 of spades only takes the 8 of spades.
• One card at a time: you can't move a run as a group.
• Empty columns accept any card.
• Eight foundation piles: two for every suit, each climbing from Ace up to King.

Why it's so hard to win casually

Skipped stock cards are gone for good

With no redeal, every card you skip in the stock is gone for good. A casual player who clicks through the stock looking for something useful often throws away the cards they'll need later.

One card at a time makes runs heavy

A long same-suit run can't be moved in one go. To shift it, you need empty columns to shuffle through, and those are scarce.

Every card has at most two places to land

Each card has at most two places to go in the tableau (one for each deck). That's why so many cards end up stuck: our program got only about a third of the cards home in an average game.

Habits that raise your odds

1. Play the Aces from the table first. In 57% of deals there's an Ace in the opening layout. Get it up before touching the stock.
2. Empty a column as early as you can. An empty column is the only way to move more than one card, so it's worth more than almost any other move.
3. Don't rush through the stock. Before turning a card, make every useful tableau move. Once a card goes past, you won't see it again unless it's playable from the waste.
4. Keep the waste pile tidy in your head. Cards pile up there, and only the top one is playable. Try not to bury a card you'll soon need under several others.
5. Build runs where you'll need them. A same-suit run that ends on a low card can go up to the foundation in one sweep later.
6. Use Undo generously. It's unlimited here, and in a game this tight, trying a different line is often the difference between a win and a loss.

How a typical game unfolds

A game of Forty Thieves usually starts with a burst of easy moves: Aces up, a few same-suit cards joined together. Then it slows down sharply, because each card has so few homes. The middle of the game is a race between the stock running down and the columns opening up. If you can empty a column before about half the stock is gone, you have a real chance. If you reach the last few stock cards with every column still full, the game is usually lost. Keep an eye on how many stock cards are left; it's the clock in this game.

What's on this page

Forty Thieves is free, with no download and no sign-up. Big cards with zoom help on a crowded two-deck table. You also get Hint, unlimited Undo, Restart, Auto Play and drag-and-drop or tap-to-move. Wins, time and moves are tracked, and you can switch off the sound, go fullscreen or change the table color. It plays in any modern browser on computer, tablet or phone.

The research behind these numbers, step by step

The play-solitaire-free-online.us team at Solitairen OOD ran this test in September 2026.

1. Rules from our game code. The Forty Thieves page runs this site's Klondike engine with its "fortythieves" setting: two decks, ten columns of four face up, a 64-card stock dealt one at a time with no redeal, same-suit building, one card at a time, and any card into an empty column.
2. Rebuilding the game. We adapted the program we built for Diplomat, another two-deck game, to these rules.
3. Numbered deals. 3,000 deals, each shuffled from a numbered seed so the test can be repeated.
4. The player. A look-ahead program that searches up to 300 positions per turn over the table and the waste, without knowing the order of the stock. If no table move makes things better, it flips over the next card from the stock. It never undoes a move.
5. Running it. It won 174 of the 3,000 deals.
6. Published comparison. Blake & Gent (2026), the largest published study of solitaire winnability, doesn't cover Forty Thieves, so we have no published figure to check against.
7. Margin of error. The 5.8% win rate has a 95% range of 5.0% to 6.7%.
8. Limits. This program is weak, so its result is a floor. We'd need a much stronger solver to say how many deals can be won with perfect play.

The code behind the test

The program is fortythieves.py, written in Python 3.11 with the standard library only. Each turn it runs a best-first search of up to 300 positions, scoring them by cards on the foundations, cards sitting on lower cards, same-suit links and empty columns, with a set of positions already seen so it doesn't loop. A shared runner spread the 3,000 deals over 19 worker processes on a 20-core machine, and the whole run took well under a minute. We worked out the 95% ranges with the Wilson score method.

We used Claude, an AI assistant by Anthropic, to help write and check the program and to draft this page. None of the numbers came from the AI; they all come from running the program.

By Admin, play-solitaire-free-online.us (Solitairen OOD). Research dated September 19, 2026.

Questions new players ask

Why is it called Forty Thieves?

The name is traditional, and we haven't found a reliable record of where it comes from, so we won't guess. The "forty" does match the forty cards dealt to the table at the start.

Do I get a second trip through the Forty Thieves stock?

No. On this site the stock is dealt once, with no redeal.

Is Forty Thieves harder than Spider?

It sits near four-suit Spider at the hard end of the site. Our programs won 5.8% of Forty Thieves deals and 0.2% of four-suit Spider deals, but both programs are weak, so neither number is the whole story.

Is there any way to shift several cards at once?

Not as a group. You move one card at a time, which is why empty columns are so valuable.

What should I try if Forty Thieves is too hard?

Diplomat is a friendlier two-deck game, and Solitaire Double is easier still.