Calculation

A solitaire unlike any other — there is almost no luck to blame, only arithmetic and foresight. Four foundations begin on an Ace, a 2, a 3 and a 4, and each one climbs by a different step: the Ace pile by ones (A,2,3,4…), the 2 pile by twos (2,4,6,8…), the 3 pile by threes, the 4 pile by fours, every count wrapping past the King and around again until it lands exactly on a King. Cards flip off the stock one at a time and you must immediately decide each one's fate: slot it onto a foundation if it is that pile's exact next value, or park it on one of just four waste piles to fetch later. The whole game is the discipline of those four piles — stack them carelessly and you bury the very card you needed three moves from now. It is famously hard and almost pure skill, so your score is simply how many of the 52 cards you can build up; getting all of them is a genuine triumph.

How to play

Four foundations sit across the top, already started on A, 2, 3 and 4. Each shows its step (+1, +2, +3, +4) and, in green, the exact value it needs next — that green target is your map, so you never have to do the wrap-around maths in your head.

Below them, one card at a time turns up from the stock. You must place that card before the next appears. There are two things you can do with it: tap a foundation, or tap a waste pile.

Tap a foundation when the stock card equals its green target — the card goes up and the foundation advances to its next value. A foundation also glows green whenever the top of a waste pile matches its target; tapping it then promotes that waste card instead. If neither the stock card nor any waste top fits, the foundation just flashes.

Tap a waste pile to stash the stock card there for later — this is how you get rid of cards you cannot yet use. You have only four waste piles and they stack downward, so a card you bury can only come back once everything on top of it is gone. Plan which pile each card goes on.

The game ends when the stock is empty and no waste top can be promoted any further. Your score is the number of cards built onto the foundations (out of 52); a full 52 means you solved it. Tap Save to send your score to the Hall of Fame, or New to deal again.

Tips & strategy

Keep each waste pile descending. The golden rule of Calculation: try to stack each pile so the values only ever go downward from bottom to top (big cards low, small cards on top). A descending pile never buries a card under a smaller one you would need first, so its cards come off in a useful order. The moment you drop a big card on top of a small one, you have likely locked that small one away for good.

Dedicate piles, don't mix blindly. With only four waste piles it helps to give each a loose purpose — for instance a home for high cards, another for a particular run you are saving. A pile that is a jumble of unrelated values is a pile you can almost never unload. Decide where a card belongs before you tap, not after.

Don't rush a card onto a foundation just because it fits. Sometimes the next card you need for one pile is the only copy, and burning it now starves a different foundation that will want that value soon. Glance at all four green targets before you play: if a value is wanted by two piles at once, think about which one truly needs it first.

Remember the wrap. Each foundation cycles past the King and keeps going (the +2 pile runs 10, Queen, Ace, 3…), so a low card late in the game is not useless — it may be exactly what a high pile needs after it loops around. Reading those wraps is what separates a score in the twenties from a full clear.