Train your brain
Improves logic, memory, and concentration.
Killer Sudoku Online
Difficulty
Error
0 / 3
Time
00:00
Score
1.850
9×9 Sudoku board. Use the arrow keys to move between cells; Home and End go to the start or end of a row; Ctrl or Command + Home/End goes to the first/last cell on the board. Keys 1–9 enter a digit in the current mode; Shift + 1–9 adds a quick Note without turning Notes on; 0, Delete, or the numpad decimal key clears a cell; N toggles Notes, A toggles Auto Candidates, and Space pauses the game.
Selected cage
Select a cell
45
Select a cell to see the cage total and possible combinations.
Levels 1–2 only guide you and do not use a hint; level 3 applies the solving step and uses 1 hint.
Tap to enter · press and hold to add a NotePress 1–9 to enter · Shift + number for quick Pencil marks
Select an empty cell to see valid candidates.
Sound & controls
Auto candidates and Notes mode are remembered separately for Classic and Killer. Pause state and game progress are not synced as preferences.
Reduce stress
Helps you relax and reduce stress.
Completely free
Unlimited play, no registration required.
Track progress
Detailed statistics and achievement tracking.
Quick guide
View the full Killer Sudoku guide
What is Killer Sudoku?
Killer Sudoku combines the rules of a 9×9 Sudoku with sum cages. Each row, column, and 3×3 block must still contain 1–9 without repeats; the digits in each cage must add up to the small number in its corner, and digits may not repeat within a cage.
An effective approach is to prioritize cages with few combinations, use rows/columns/blocks to eliminate digits, then apply the Rule of 45 when a region is close to a known sum. Start on Easy if you are new to reading cages.
1Keep the standard Sudoku row, column, and 3×3 block rules.
2Add the cells in each cage to reach the target shown in its corner.
3No repeated digits within the same cage.
45Use the total of 45 in a row, column, or block to derive the missing digit.
Killer Sudoku learning path
Learn cages first, then use the Rule of 45
Start with cages that have very low or very high sums because they allow fewer digit combinations. Then combine those cage possibilities with the normal row, column and 3×3 box rules instead of treating each cage as a separate arithmetic problem.
When most of a row, column or box is covered by known cage sums, use the Rule of 45 to calculate the missing total. This turns cage arithmetic into candidate eliminations that the regular Sudoku rules can finish.
Killer Sudoku FAQ
Killer Sudoku questions
What is Killer Sudoku?
Killer Sudoku keeps the normal 9×9 Sudoku rules and adds cages. The digits inside each cage must add up to the printed target, and a digit cannot repeat within the same cage.
What is the Rule of 45 in Killer Sudoku?
Every row, column and 3×3 box contains the digits 1 through 9 exactly once, so each complete region totals 45. Comparing that total with cage sums can reveal the value or combined sum of cells that cross a region boundary.
Which cage combinations should I learn first?
Start with extreme sums that have very few combinations. Examples include two cells totaling 3 as 1+2, two cells totaling 17 as 8+9, three cells totaling 6 as 1+2+3, and three cells totaling 24 as 7+8+9.
Can I play Killer Sudoku online for free?
Yes. You can play Killer Sudoku free in your browser, switch difficulty, use notes and hints, save an unfinished game locally, and try the separate Daily Killer challenge.
Advanced Killer Sudoku
How to Play Killer Sudoku
Killer Sudoku strategies to learn
Start with how to read cages and sums, then learn the Rule of 45. Each guide focuses on one reasoning group so you can practice it separately instead of reading one overly long article.
Killer Sudoku strategy: how to read cages and eliminate combinations
Practical Killer Sudoku strategy: prioritize cages with few combinations, combine row/column/block rules, manage candidates, and use sums to open the board.
Rule of 45 in Killer Sudoku: How to Calculate Innies & Outies
Understand the Rule of 45 in Killer Sudoku: why every row/column/block totals 45, how to calculate excess or missing sums, and how to use innies/outies safely.
How to solve Sudoku: techniques from basic to advanced
A systematic Sudoku solving path: scan singles, manage candidates, use pairs, locked candidates, and advanced patterns without guessing.