Every killer sudoku online here is made by our own generator. The killer sudoku solver proves each grid has exactly one answer and rates it by the hardest technique its step-by-step logic needs, so the level you pick is measured, not guessed. A daily killer sudoku at each level is the same for everyone, and New puzzle gives you as many free grids as you like.
How to play killer sudoku
The usual sudoku rules apply: each row, each column and each 3 by 3 box holds the digits 1 to 9 once. On top of that the grid is split into cages, shown with dotted outlines. The small number in a cage is the sum of its digits, and a digit never repeats inside a cage. Most killer puzzles start with an empty grid, so the cage sums are your only clues.
Tap a square and then a digit. Turn on Pencil to write small candidates; placing a digit removes it from the pencil marks of the squares it sees. Digits that clash with another digit in the same row, column or box turn red at once.
The three levels
- Easy: cages of two or three cells and a few given digits. The engine rates it Easy or Medium: singles, pointing pairs and cage combinations are enough.
- Medium: the same small cages with at most four given digits, rated Hard. Expect the 45 rule.
- Hard: cages of up to five cells, at most two given digits, rated Hard to Master, still without any trial and error.
Medium and hard grids come from a bank of puzzles built this way and checked again by our tests; easy grids are made fresh in your browser.
Killer sudoku tips
- Unique sums: a two-cell cage of 3 is always 1 and 2, of 17 always 8 and 9. Three cells adding to 6 are 1, 2, 3; to 24 they are 7, 8, 9. The combination chart lists every case.
- The 45 rule: each row, column and box adds up to 45. Add the cages that lie fully inside a box; the difference to 45 is the value of the cells that stick out or are missing.
- Combine cages with lines: if two cages cover a whole row except one cell, that cell is 45 minus their sums.
- Write the options: pencil the possible digits of tight cages early. A cage of 4 in two cells is 1 and 3, never 2 and 2.
Hints and statistics
Hint shows the next step the solver would take, in words, from naked singles to cage combinations and innies and outies. When a step only removes candidates, it updates your pencil marks and says so. A wrong digit is taken out first. Your games, best and average time and the streak of days you solved the daily killer sudoku are kept per level in this browser, and Challenge a friend sends the exact grid.
New to the sums? Start with how to solve sudoku and the sudoku techniques page. Plain grids are on our sudoku online page.
Solver tested . Found a problem? Tell us.
Questions
Is this killer sudoku free?
Yes. Every grid, the daily killer sudoku and the hints are free, with no sign-up. Your progress stays in your browser.
Can a digit repeat in a killer sudoku cage?
No. Digits inside one cage are all different, and the cage still follows the row, column and box rules.
What is the 45 rule?
The digits 1 to 9 add up to 45, so every row, column and box does too. Comparing that total with the cages inside a house tells you the sum of the few cells left over, often a single digit.
When does the daily killer sudoku change?
At midnight on your device. Each level has its own daily grid, made by our generator from the date, so it is the same for everyone that day.
Do I ever have to guess?
No. Each grid was checked to be solvable by the step-by-step solver without trial and error, and to have exactly one answer.