Calcudoku

Calcudoku is a math logic puzzle that mixes the row and column rules of Sudoku with simple arithmetic. You fill a square grid so that no number repeats in any row or column, and every outlined cage hits its target. Play Calcudoku online free in your browser with no download or sign-up. Every puzzle has exactly one solution and can be finished by logic alone, without guessing.

How to play

The grid is a square from 4×4 up to 9×9. Thick lines split it into cages, and the small clue in the top left corner of each cage gives its target and operation.

• Rows and columns: on an N by N grid, each row and each column holds the numbers 1 to N exactly once. A 6×6 grid uses 1 to 6.
• Addition and multiplication: a 9+ cage adds up to 9, and a 24× cage multiplies to 24. These cages can have two or more cells.
• Subtraction and division: these cages always have two cells, in either order. A 2− cage holds two numbers that differ by 2, such as 5 and 3. A 3÷ cage holds two numbers where one is three times the other, such as 6 and 2.
• One-cell cages: a single cell with no operation sign is a free number. Write it in.
• Repeats inside a cage: a number can appear twice in one cage only when the copies sit in different rows and columns, as in an L-shaped cage.

The puzzle is solved the moment every cell is filled and all the rules hold. The timer stops and your time goes into your statistics.

Sizes, operations and the daily puzzle

Pick a grid size from 4×4 to 9×9 and the operations the cages may use: addition only, addition and subtraction, or all four. Press Daily for the puzzle of the day at those settings. Anyone who picks the same options on the same date gets the same grid. Press New puzzle for unlimited practice puzzles.

Controls and tools

• Numbers: click or tap a cell, then tap the number pad or press a number key. Arrow keys move, and Backspace or Delete clears a cell.
• Notes: press N or the Notes button for pencil marks, or hold Shift while typing a number. A placed number is removed from the notes in its row and column.
• Hint: finds the next logical step and explains it in plain English, for example that a cell must be 4 because its row already has 1 and 3 and its cage cannot use 2. It fills that cell, highlights the cells behind the reasoning and adds 15 seconds to your time. If there is a mistake on the board, the hint points it out first.
• Check, conflicts, Undo and Redo: Check marks every wrong number. With Show conflicts on, numbers turn red when they repeat in a line or when a cage can no longer reach its target. Z and Y undo and redo.
• Pause: press P or Esc. The grid is hidden while the timer is stopped, and the game also pauses when you switch tabs.

The Stats panel shows puzzles played and solved at each size, best and average times and your daily streak (days in a row with a solved daily puzzle). Unfinished puzzles are saved in your browser.

Calcudoku tips

• Start with the giveaways. Fill in the one-cell cages, then look for cages with only one possible pair, such as 3+ (always 1 and 2).
• Factor the products. A two-cell 15× cage can only be 3 and 5. A product that is not a multiple of 5 rules out 5 for every cell in that cage.
• Use the row total. Every row and column adds up to 1 + 2 + … + N, which is 21 on a 6×6 grid. If the addition cages inside a row make 17, the cells left over must make 4.

FAQ

Is this Calcudoku game free?

Yes. It is free with no account and nothing to install.

Does every puzzle have only one solution?

Yes. A solver counts the solutions of each puzzle, and it is only used if there is exactly one. It is also checked to make sure it can be solved step by step, so you never need to guess.

How is Calcudoku different from Sudoku?

Both ban repeats in rows and columns, but Calcudoku has no 3×3 boxes and gives arithmetic clues instead of starting numbers. Try our free Killer Sudoku, which adds sum cages to a classic grid, or the original Sudoku.

Can I play on my phone?

Yes. Tap a cell and use the on-screen number pad. The grid scales to fit small screens and does not scroll the page while you play.