# Killer Sudoku: Rules and How to Play (Beginner's Guide)

**Quick answer:** Killer Sudoku is classic Sudoku plus simple addition. The grid is split into dashed **cages**, each labelled with a target sum; the cells in a cage must add up to that number **without repeating a digit** — on top of the usual rule that every row, column, and 3x3 box holds 1 to 9 once. There are no starting numbers, so the cage sums are your clues.

If you have mastered [classic Sudoku](/guides/how-to-play-sudoku), Killer Sudoku is the most popular next step. Here is how it works.

## The rules of Killer Sudoku

Killer keeps every classic Sudoku rule and adds one layer:

1. **Rows, columns, and boxes:** each must contain 1 to 9 exactly once — same as always.
2. **Cages:** the grid is divided into dashed-outline groups of cells. The small number in a cage's corner is the **sum** its cells must add up to.
3. **No repeats in a cage:** a digit cannot appear twice inside the same cage (even if the box rule would otherwise allow it).

Crucially, a Killer puzzle usually starts **empty** — no given digits. The cage sums are the only clues, and that is enough.

## Start with the small cages

Low-cell cages with extreme sums have very few combinations, so they are the best foothold:

- A **2-cell cage summing to 3** can only be **1 + 2**.
- A **2-cell cage summing to 17** can only be **8 + 9**.
- A **3-cell cage summing to 6** can only be **1 + 2 + 3**.

You may not know the order yet, but you have narrowed those cells to two or three candidates — exactly like a naked pair in classic Sudoku.

## Use the 45 rule to break in

Every row, column, and 3x3 box adds up to **45** (1+2+…+9). This is Killer's signature trick:

> If cages neatly fill a row, column, or box except for one stray cell, add up those cage sums and subtract from 45. The remainder is that cell's value.

The same idea works when a cage pokes just one cell out of a box — the "innie" or "outie" — letting you pin down a single number.

## Then it plays like Sudoku

Once cage logic gives you a few placements and candidate pairs, the puzzle solves with the [same techniques as classic Sudoku](/guides/intermediate-sudoku-strategies) — hidden singles, naked pairs, pointing groups. The cages simply hand you a head start that a normal grid never would.

Ready to try one? Killer Sudoku is a built-in mode in the [Sudoku Aura app](https://apps.apple.com/us/app/id6760272815). For the full family of variants, see our guide to the [types of Sudoku](/guides/types-of-sudoku), or [play a free classic puzzle](/) to warm up.