Killer Sudoku rules, cage strategy and solving techniques

What is Killer Sudoku?

Killer Sudoku keeps every classic Sudoku rule and adds dashed cages with printed totals. On DIGIGMA the live board is 9×9. The cages are the clues. There are usually no given digits.

A cell is still one square. A box is still a 3×3 block. A cage is a group of cells that must add up to a printed sum.

Goal of the game

Fill every cell with 1–9 so each row, column, and 3×3 box is unique, and every cage adds to its printed total. There is one solution. You do not need to guess.

Rules

• All Sudoku rules apply: 1–9 once in every row, column, and 3×3 box.
• The digits in a cage add up to the total printed on that cage.
• A digit does not repeat inside a cage.

The no-repeat cage rule is part of DIGIGMA Killer. A two-cell cage cannot be 4+4 even if the sum would match.

How to start a grid

Open an Easy board from available grids. Tap a cell, then pick a digit. Turn on Draft when a cage still has more than one mix.

Start with the smallest cages and the most constrained boxes. A 2-cell cage with a rare sum is usually easier than a long winding cage.

A step-by-step solving method

1. Spot cages with very few combinations (3, 4, 16, 17 on two cells).
2. Write the possible mixes in Draft.
3. Drop any mix that repeats a digit already taken in the row, column, or box.
4. Cross the cage with Sudoku: a cage inside one box must also obey that box.
5. When a cage is almost complete, subtract the known digits and finish it.
6. After each placement, hunt ordinary Sudoku singles.
7. Repeat. Killer is cage logic plus Sudoku, not cages alone.

Useful cage combinations

You do not need every combination memorised. These two-cell sums appear constantly and have few mixes.

Cross the cage with a line or box

If the 1 from a 1+2 cage cannot sit in one of the two cells because that row already has a 1, the 1 is forced into the other cell. The same idea works with a 3×3 box.

When you’re stuck

• Recount the remaining total on cages that already have a digit.
• Cross each leftover mix with the row, column, and box.
• Finish cages that have only one mix left.
• Return to ordinary Sudoku singles — they often appear after a cage placement.
• Do not guess. The next forced cell is on the board.

Common mistakes

• Looking only at cages and forgetting Sudoku.
• Allowing a repeated digit inside a cage.
• Keeping a sum mix that is already impossible in the box.
• Treating a long cage as more important than a tight 2-cell cage.

Practical tips

• After each digit, subtract it from the cage total and shrink the mix.
• A cage that sits inside one box is usually easier than a cage that crosses two boxes.
• Draft both the cage mix and the Sudoku candidates. They constrain each other.
• Play from today’s Killer grids once the method feels familiar.

FAQ

Is Killer Sudoku harder than Sudoku?

It asks for one extra skill — cage sums — but Easy Killer still starts with forced mixes. You do not need speed arithmetic.

Do cages allow repeated digits?

Not on DIGIGMA. A digit never repeats inside a cage.

Should I solve cages or Sudoku first?

Start with tight cages, then immediately apply Sudoku. The two views take turns.

Do I need arithmetic skills?

Only small additions. The useful mixes above cover most Easy and Medium boards.

What should I do when I get stuck?

Recount leftover cage totals, drop impossible mixes, then hunt Sudoku singles.