Killer Sudoku

There are three rules:

• Every row, column and 3 by 3 box holds the numbers 1 to 9 once, just like normal Sudoku.
• The numbers in a cage add up to the cage's total.
• A number can't appear twice in the same cage.

Every puzzle here is checked by a solver before you see it, so it has exactly one answer and can be finished without guessing.

How to solve Killer Sudoku

1. Look for cages with only one answer. A two-square cage with a total of 3 can only be 1 and 2. A total of 17 can only be 8 and 9. Start with these.
2. Use single-square cages. A cage of one square tells you the number directly. Fill it in first.
3. Use the rule of 45. Each box, row and column adds up to 45. Add up the cages that sit fully inside a box and the gap tells you what is left.
4. Narrow down the other cages. A two-square cage of 10 could be 1 and 9, 2 and 8, 3 and 7 or 4 and 6. Numbers already in that row, column or box rule some of these out.
5. Switch to normal Sudoku. Once a few numbers are placed, ordinary scanning along rows, columns and boxes takes over.

Cages with only one answer

Some totals can only be made one way. These are the best places to start. The numbers can go in either order inside the cage, but you know exactly which numbers they are.

Cage size	Smallest totals		Largest totals
2 squares	3 = 1 + 2	4 = 1 + 3	16 = 7 + 9	17 = 8 + 9
3 squares	6 = 1 + 2 + 3	7 = 1 + 2 + 4	23 = 6 + 8 + 9	24 = 7 + 8 + 9
4 squares	10 = 1 + 2 + 3 + 4	11 = 1 + 2 + 3 + 5	29 = 5 + 7 + 8 + 9	30 = 6 + 7 + 8 + 9
5 squares	15 = 1 + 2 + 3 + 4 + 5	16 = 1 + 2 + 3 + 4 + 6	34 = 4 + 6 + 7 + 8 + 9	35 = 5 + 6 + 7 + 8 + 9

Many other totals have just two or three options. A two-square cage of 5 is either 1 and 4 or 2 and 3. A two-square cage of 15 is either 6 and 9 or 7 and 8. Learning these speeds you up a lot. Our Killer Sudoku combinations chart lists every option for two and three square cages.

The rule of 45

The numbers 1 to 9 add up to 45. That means every row, every column and every box also adds up to 45. It sounds simple, but it is the most useful idea in Killer Sudoku.

Say the cages fully inside the top left box add up to 38, and one square of that box belongs to a cage that sticks out into the next box. That single square must be 45 minus 38, which is 7. The same trick works across two or three rows or columns at once, where the totals add up to 90 or 135.

The four levels

Easy	Small cages of two and three squares, plus a few starting numbers.
Medium	Cages of two and three squares. No starting numbers.
Hard	Cages of up to four squares. You will need the rule of 45.
Expert	Cages of up to five squares, with more totals that can be made several ways.

Tips for this page

Selecting a square shades its row, column, box and cage, so you can see what is already used. Notes sit a little lower in the square to leave room for the cage total. When a whole cage is right, it gives a short flash.

Questions people ask

More Sudoku games