Killer Sudoku for Beginners

By Andrew Boyko, developer of CageDoku · Updated October 23, 2026

If you can solve a classic Sudoku, you already know most of Killer Sudoku. The only new ingredient is the cage: a dotted group of cells with a target sum. This page takes you from zero to your first solved puzzle without any guessing.

What you are looking at

There are almost no starting digits. Instead, the grid is split into dotted cages and each cage shows a sum in its corner. The digits in a cage must add up to that sum and cannot repeat. Rows, columns and boxes still contain each digit once. That is all of it; the full rules fit on one screen.

Your first move: unique cages

Some cages can only be filled one way. Learn these and you will have candidates in half the grid within a minute:

• 2 cells, sum 3: 1-2
• 2 cells, sum 4: 1-3
• 2 cells, sum 16: 7-9
• 2 cells, sum 17: 8-9
• 3 cells, sum 6: 1-2-3
• 3 cells, sum 7: 1-2-4
• 3 cells, sum 23: 6-8-9
• 3 cells, sum 24: 7-8-9
• 4 cells, sum 10: 1-2-3-4
• 4 cells, sum 11: 1-2-3-5
• 4 cells, sum 29: 5-7-8-9
• 4 cells, sum 30: 6-7-8-9

You do not need to memorise them in one go. Keep the chart open, or use the calculator, until they stick.

Your second move: the 45 rule

Every row, column and box sums to 45. When cages cover all but one cell of a region, that one cell is 45 minus their sum. Read the 45 rule once and you have the technique that solves most Gentle and Moderate puzzles.

Your third move: remove candidates

A 3-cell cage with sum 8 is either 1-2-5 or 1-3-4. That means a 1 is certain in the cage, and 6, 7, 8 and 9 are impossible there. Crossing out impossible candidates is most of the work in Killer Sudoku.

Do I have to guess?

No. If you ever feel you need to guess, a technique is being missed. In CageDoku the hint button names the technique and highlights the cells so you can learn it. Start on Gentle, graduate to Moderate once the 45 rule feels natural, and try a 6×6 puzzle when you want a quick one.

Next steps

When you are comfortable, read eight proven techniques, and look at the other Sudoku variants: Thermo and Diagonal are friendly if you want to stay close to classic rules.

Frequently asked questions

Is Killer Sudoku good for beginners?

Yes, if you start on a Gentle or 6×6 puzzle and keep a combination chart nearby.

Do I need to be good at maths?

Only simple addition up to 45. The work is mostly elimination.

What if I get stuck?

Use a hint. In CageDoku a hint explains the technique, not just the digit.

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