Calcudoku

How to use it

• Play — a puzzle at the chosen size and level, one you have not played yet.
• Daily — one puzzle per date, numbered from 21 October 2026, larger and harder through the week: Monday 5×5 Easy, Tuesday 6×6 Easy, Wednesday 6×6 Medium, Thursday 7×7 Medium, Friday 7×7 Hard, Saturday 8×8 Hard, Sunday 6×6 Medium. A daily you are playing at midnight stays on the page until you finish it. Opened on a later day, the page shows that day's puzzle instead, and an earlier one you had started counts as played, not won.

A cage shows its target and operation in its top-left corner: 12× means its digits multiply to 12, 3− that the larger of its two digits less the smaller is 3, and 2÷ that the larger divided by the smaller is 2. A cage of one cell shows its digit. − and ÷ only ever join two cells.

Select a cell, then a digit on the pad or the keyboard; the arrow keys move, Backspace clears, N switches notes and Shift with a digit adds a note. Auto fills every empty cell with the digits its cage allows, less those its row and column hold. The combination helper lists the digits that can fill the selected cell's cage, each set once, struck through once the grid rules it out.

Hint first points out a wrong digit, then finds the simplest next step and explains it, and where no technique finds one, offers to reveal a cell; the second press applies it. A game finished after a hint, a revealed cell or with mistakes shown counts as played, not won, and ends your streak. Stats are kept per size and level.

How the puzzles are made and solved

Cage combinations. List the ways a cage can make its target: in a 6 × 6, 12× in two cells side by side is 2 × 6 or 3 × 4, so those cells hold only 2, 3, 4 or 6. A digit may repeat in a cage whose cells are not all in one row or column, so an L-shaped 3-cell cage of 4× can be 1 × 2 × 2 or 1 × 1 × 4, while three cells in a row can only be 1 × 2 × 3 for 6×.

Cage and line. When every way to fill a cage puts a digit in one row or column, that line's digit is in the cage, and no other cell of the line can hold it. Line sums. Each row adds to 1 + 2 + … + N (21 in a 6 × 6). Subtract the cages whose sums are known, and the cells left over make up the rest.

The puzzles come from a fixed bank of up to 300 per size and level. Each starts from a random Latin square cut into cages of one or two cells, and neighbouring cages merge one pair at a time, each merged cage drawing its operation afresh, each merge kept only while the puzzle can still be solved by logic within its level. A path solved by logic alone also proves the puzzle has one solution. Cages reach 4 cells, or 5 at 8 × 8 and 9 × 9, and a product never exceeds 9,999, so every clue fits its cell.

Worked hints

Quick reference

Frequently asked questions

See also

• Killer Sudoku — for sum cages on a full 9 × 9 Sudoku.
• Sudoku — for the classic puzzle with givens.
• Kakuro — for sums across and down, crossword style.