Forty Thieves Solitaire: the two-pack challenge with no second chances
Forty Thieves is a proper challenge. Two packs, forty cards dealt face up in ten columns, one trip through the stock and not a single redeal. Cards move one at a time and build only in suit. It is a demanding game, and every win feels properly earned.
If you enjoy a challenge for a long evening, this is your game. This page covers the layout, the rules as played here, the habits that make the difference, and an honest look at what our testing found.
Dealing the forty thieves
- Two packs are shuffled together: 104 cards.
- Ten columns of four cards each, all face up. Those are the forty "thieves".
- A 64-card stock holds the rest, dealt one card at a time onto a waste pile.
- Eight foundations, two for each suit, built from Ace to King.
The rules of Forty Thieves
Your goal
Get all 104 cards onto the eight foundations. Each suit has two piles running from Ace up to King.
Building in suit across ten columns
- Build downwards in suit: the 8 of clubs goes on the 9 of clubs, and nowhere else.
- Move one card at a time. Runs cannot be lifted as a group.
- Any card may be placed in an empty column.
The stock and waste
- Turn the stock one card at a time onto the waste. The top waste card may be played to a column or a foundation.
- There is no redeal. When the stock is used up, that is all the help you get.
Why Forty Thieves is so tough
Three rules pull in the same direction.
In-suit building means each card has only two possible landing spots on the whole table (the two matching cards one rank higher), rather than the four you would have in a colour-alternating game.
One card at a time means a long run cannot be shifted without spare space, and spare space is rare.
A single pass through the stock means that a card you let go by is gone for good, buried under the waste.
Put together, those rules mean that your early moves shape the whole game. Get them right and it opens up; rush them and it can close down very quickly.
Habits that catch the thieves
Take time over the opening
All forty tableau cards are face up, so you can plan properly before you touch the stock. Look for Aces first: in our testing, 57% of deals had at least one Ace playable straight from the opening tableau.
Work towards an empty column
An empty column is worth more than almost anything in Forty Thieves. It can take any card, and it gives you somewhere to break up an awkward stack. Choose one short, easily cleared column and focus on it early.
Think before turning each stock card
Every card that goes onto the waste covers the one before it. Before you turn a card, ask whether the current waste card has anywhere to go. If it does, and playing it does not hurt your tableau, play it first.
Avoid building long runs in the wrong places
Since runs move one card at a time, a long run sitting on top of a card you need can be a real trap. Build where it will help the foundations, not just wherever a card fits.
Use Undo to test a plan
Forty Thieves punishes guesses. When you are unsure, try a line and undo it if it goes badly. Nobody here is keeping score but you.
What our testing showed, and what it did not
We set a computer player loose on 3,000 numbered deals. It sees only what you would see, does not know what is coming in the stock, looks a few hundred positions ahead before each move, and never undoes anything.
| Result on 3,000 deals | Figure |
|---|---|
| Games won by the computer player | 5.8% (95% range 5.0% to 6.7%) |
| Cards it got home, on average | about 34 of 104 |
| Moves in its winning games (including stock turns) | about 277 |
| Deals with an Ace playable at the start | 57% |
Please read the 5.8% carefully. It is not how winnable Forty Thieves is. It is how often a fairly simple program won without ever undoing a move. It is a floor, and a low one: a patient human who plans and uses Undo should do noticeably better. We have not yet run a solver on this game, so we cannot tell you the true share of winnable deals. What the figure does show is that Forty Thieves does not forgive careless play.
Forty Thieves on solitaire-free.nz
Forty Thieves is free to play on solitaire-free.nz in any modern browser, on a computer, tablet or phone. There is nothing to download, no sign-up and no email. The cards are large and clear, and the zoom control helps on a table of 104 cards. You can drag cards or tap a card and then where it should go. Hint, unlimited Undo, Restart and Auto Play are all available, and the game tracks your wins, time and moves. You can switch the sound off, go fullscreen and pick a table colour.
Where our numbers come from, one step at a time
The solitaire-free.nz team ran this study in September 2026, using the Forty Thieves rules from this page.
- We took the rules from the game code. Two packs, ten face-up columns of four, a 64-card stock turned one card at a time with no redeal, in-suit building, single-card moves, any card in an empty column.
- We built a program that plays by exactly those rules.
- We dealt 3,000 numbered games, each from a seed number so the test can be run again with the same cards.
- We chose a look-ahead player. Before every move it looks up to 300 positions ahead using only the cards it can see, and it does not know the order of the stock. When nothing improves its position, it turns the next stock card.
- We counted results: games won, cards reaching the foundations, and moves in winning games.
- We looked for published research. We found no published figure for Forty Thieves to compare with.
- We worked out the margin of error. The 5.8% has a 95% range of 5.0% to 6.7%.
- We are clear about the limits. This player is weak for a game this demanding, so its result is a low floor, not the real odds.
The nuts and bolts
The code is Python 3.11 with only the standard library, in a module called fortythieves.py. It adapts the look-ahead player we built for Diplomat: before each move it runs a small best-first search of up to 300 positions, scoring each one by cards on the foundations, same-suit links, empty columns and cards left stuck above lower cards, and it keeps a set of positions already seen so it does not waste effort. A shared runner spreads the deals across the computer's processor cores with multiprocessing, and every deal is shuffled from a numbered seed. Percentages carry Wilson score intervals.
We had help from Claude, an AI assistant made by Anthropic, in writing and reviewing the code and drafting this page. The AI did not make up any numbers: everything comes from running the program, and the team checked the study against published research before publishing.
By Admin, solitaire-free.nz. Study date: September 2026.
Frequently asked questions
How many cards are dealt at the start?
Forty: ten columns of four, all face up. The other 64 cards wait in the stock.
Can I go through the stock more than once?
No. Forty Thieves has one pass through the stock and no redeal.
Can I move a run of cards together?
No. In this game cards move one at a time, so plan your runs carefully.
Is 5.8% really the chance of winning?
No. That is how often a simple computer player won without using Undo. Thoughtful play wins more often; we have not yet measured how much more.
What should I play for something gentler?
Try Solitaire Double for a friendlier two-pack game, or Diplomat Solitaire, which uses a similar layout. See all our games on the games page and read more on the blog.