What is Killer Sudoku?
Killer Sudoku (also called Sum Sudoku) is a logic puzzle that combines Sudoku with Kakuro-style sum constraints. The grid starts with no given digits. Instead, it is divided into cages—outlined groups of cells with a small number indicating the sum.
Each cage must be filled with unique digits (no repeats within a cage) that add up to the cage's target sum. At the same time, standard Sudoku rules apply: every row, column, and 3×3 box must contain the digits 1-9 without repetition.
Every puzzle has exactly one solution. PencilGrid's generator guarantees unique solutions. Difficulty ratings reflect cage complexity, overlap patterns, and the depth of sum-based elimination required. The daily difficulty rotates throughout the week: Monday, Wednesday, and Friday are Easy; Tuesday, Thursday, and Saturday are Medium; Sunday is Hard. Practice mode offers unlimited puzzles at your chosen difficulty.
Features
Daily Puzzles
New Killer Sudoku every day at midnight UTC. Build a streak by solving consecutive days.
Practice Mode
Unlimited puzzles at Easy, Medium, and Hard difficulty. Perfect for learning cage logic and sum patterns.
Notes Mode
Pencil in candidate numbers (notes) in each cell. Essential for tracking possible cage combinations.
Cage Sum Validation
Real-time cage sum tracking. See which cages are complete, which are still open, and which have errors.
Error Checking
Check your work at any time. Conflicts and cage errors are highlighted so you can find mistakes.
Undo/Redo
Full undo/redo stack. Experiment with cage combinations freely without fear of losing progress.
How to Play
The Rules
1.
Fill the grid with digits 1-9 following standard Sudoku rules: each row, column, and 3×3 box must contain all digits without repetition.
2.
The grid is divided into cages (groups of cells outlined with dashed borders). Each cage has a small number showing the target sum.
3.
Within each cage, all digits must be different (no repeats), and they must add up to the cage's sum.
4.
Unlike classic Sudoku, there are no given digits at the start. You solve using cage sums and Sudoku elimination logic.
Basic Strategy
Start with small cages (2-3 cells) where there are only a few possible digit combinations. For example, a 2-cell cage with sum 3 must be 1+2. Use notes mode to track candidates. Look for cages that overlap in the same row, column, or box—these create elimination opportunities. The puzzle always has exactly one solution.
Common Cage Combinations
Recognizing these patterns speeds up solving:
•
2-cell cages: Sum 3 = {1,2}, Sum 4 = {1,3}, Sum 16 = {7,9}, Sum 17 = {8,9}
•
3-cell cages: Sum 6 = {1,2,3}, Sum 7 = {1,2,4}, Sum 23 = {6,8,9}, Sum 24 = {7,8,9}
•
Unique sums: When a cage has only one possible combination, fill those candidates immediately.
Frequently Asked Questions
What is the difference between Killer Sudoku and regular Sudoku?
Killer Sudoku has no given digits at the start. Instead, the grid is divided into cages (outlined groups of cells) with sum clues. Each cage shows a target sum, and you must fill the cage with unique digits that add up to that sum while following standard Sudoku rules.
Are killer sudoku cages allowed to repeat numbers?
No. Within a single cage, all digits must be different. This is the key constraint that makes Killer Sudoku solvable without given digits. However, the same digit can appear in different cages within the same row, column, or box, as long as standard Sudoku rules are satisfied.
Do killer sudokus have a unique solution?
Yes. Every Killer Sudoku puzzle on PencilGrid has exactly one solution. Our generator guarantees unique solutions.
Is PencilGrid Killer Sudoku completely free?
Yes, all Killer Sudoku puzzles on PencilGrid are completely free. No account, subscription, or payment required. Play as much as you want.
When does the new daily puzzle become available?
A new daily Killer Sudoku puzzle is published every day at midnight UTC. You can complete previous dailies even if you missed them.
Explore More
How to Play Killer Sudoku
Complete rules guide and solving strategies for cage-based puzzles.
Daily Puzzle Info
Learn about the daily puzzle format, difficulty rotation, and streak tracking.
Solving Techniques
Master cage combinations, the 45 rule, and advanced solving methods.
Play Today's Puzzle
Solve today's daily Killer Sudoku and maintain your streak.
Practice Mode
Unlimited puzzles at Easy, Medium, and Hard difficulty levels.
Printable Puzzles
Download and print Killer Sudoku puzzles at all difficulty levels.
Play Classic Sudoku
Try the traditional 9×9 Sudoku with given digits and no cages.
Play Nonogram
Reveal hidden pictures using row and column clues in this logic puzzle.