Killer Sudoku

How to Play Killer Sudoku

Killer Sudoku keeps the row, column, and 3×3 block rules of Sudoku, while adding cages with target sums. Digits may not repeat within the same cage.

Play Killer SudokuView Rule of 45
Rules

Killer Sudoku has four core rules

Row

Each row contains 1–9 without repeats.

Column

Each column contains 1–9 without repeats.

3×3 block

Each block contains 1–9 without repeats.

Cage

Match the corner total with no repeated digits in the cage.

Cage

Read the cage total before looking at individual cells

A cage can contain two, three, or more edge-connected cells. The small number in the corner is the total of all cells in the cage.

3 / 2 cells1 + 2
17 / 2 cells8 + 9
6 / 3 cells1 + 2 + 3
24 / 3 cells7 + 8 + 9
Tip: Cages with very low or very high sums usually have fewer combinations, making them good starting points.
Combination

Eliminate combinations using rows, columns, and blocks

For example, a two-cell cage totaling 10 could be 1+9, 2+8, 3+7, or 4+6. But not every digit set with the right total fits every cell: the row, column, 3×3 block, and digits already used in the cage eliminate more placements.

  • Do not repeat a digit within the same cage.
  • Use Sudoku rules to eliminate digits already present in the row/column/block.
  • Distinguish a “digit set” from a “placement”: the same set of digits may have only a few valid positions left.
  • If a digit appears in every valid placement of a cage, it is mandatory for that cage even if you do not yet know the exact cell.
In the game: The helper beside the board shows the number of valid placements, remaining digit combinations, and digits that must appear in the selected cage.
Region–cage intersection

Lock candidates when a cage intersects a row, column, or block

If a required cage digit can only lie in the part of the cage that falls within one row, column, or block, that digit can be eliminated from other cells in that region outside the cage. The reverse also applies: if every position for a digit in a region lies inside the same cage, you can eliminate it from the rest of that cage.

  • Cage → region: a forced digit is locked to one row/column/block.
  • Region → cage: every position for the digit in the region lies in the same cage.
  • This is a candidate elimination, not an immediate answer placement.
Rule of 45

Every row, column, and 3×3 block always totals 45

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45

Innie: if cages fully inside a region cover 8 cells, the remaining cell equals 45 minus the total of those cages. Outie: if cages touching a region cover all 9 cells and extend by exactly one cell, the outside cell equals the total of the touching cages minus 45.

Important: Only apply this when cage boundaries clearly identify what is inside and outside. Do not count a cage twice.
Start

Recommended deduction order

  1. 1

    Find cages with few placements

    Prioritize cages with few digit sets or with a mandatory digit that appears in every valid placement.

  2. 2

    Combine Sudoku rules

    Continue eliminating with row, column, and block rules, and track the position of each candidate within the cage.

  3. 3

    Find region–cage interactions

    When a candidate is locked in an intersection, eliminate it from the remaining part before guessing a digit.

  4. 4

    Use the Rule of 45

    Check both innies and outies when cages cover nearly an entire row, column, or block.

Quick input: Shift + number on a keyboard or press and hold a number key on a touchscreen to enter a quick Pencil mark; cage rules still block invalid candidates.

Try a Killer game now

Start on Easy to get comfortable with cages before moving to advanced sum techniques.

Play Killer Sudoku
Advanced Killer Sudoku

Killer Sudoku strategies to learn

How to Play Killer Sudoku

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.