1geplay solving guide

Killer Sudoku Rules & How to Play

The little numbers tell you what a group of cells adds up to. The sudoku rules tell you where each digit can go. Use both together, and an empty-looking grid starts giving you answers.

What Is Killer Sudoku?

Killer Sudoku combines a standard 9×9 sudoku grid with arithmetic clues. Dashed outlines divide the cells into cages, each labelled with a total. You fill the grid using digits 1–9 while satisfying both the usual sudoku rules and those cage totals.

Ordinary sudoku usually begins with digits already in place. Killer Sudoku can begin with no filled cells at all: its totals supply the opening clues. The arithmetic is simple addition; deciding where the digits belong is the puzzle.

The Rules of Killer Sudoku

The normal sudoku rules still apply

Use each digit from 1 to 9 once in every horizontal row, vertical column and thick-bordered 3×3 box. A number that fits its cage still cannot duplicate a digit in any of those three units.

What the small number on a cage means

The small number is the sum of every cell inside that dashed outline. A two-cell cage marked 3 must contain 1 and 2. The total belongs to the whole cage, not just the cell beside the label.

No repeats inside a cage

Digits cannot repeat within a cage. A two-cell cage totalling 4 therefore contains 1 and 3, never 2 and 2. This restriction applies even if its cells are in different rows, columns or boxes.

Cages can cross into another box

A dashed cage and a thick-bordered box are different groups. A cage may cross a box boundary or have an irregular shape. Keep following its dashed outline for the sum, and keep following the thick lines for the sudoku restrictions.

Cage Combinations Worth Memorising

A combination is an unordered set of different digits. Extreme totals often give you just one set, so they make useful starting points. These tables show combinations forced by the cage size and total alone.

Two-cell cages with one possible combination

Three-cell cages with one possible combination

Middle totals leave more choices. For instance, two cells totalling 7 can be 1 + 6, 2 + 5 or 3 + 4. A placed digit can rule out candidates in the cells that share its row, column or box.

A known combination is not a known placement. Knowing that a cage contains 1, 2 and 4 does not tell you which cell gets each digit. If one cell's row already contains 4, that cell cannot be 4; check its column and box to narrow it further.

The Rule of 45, Explained

The digits 1 through 9 add up to 45. Every complete row, column and 3×3 box therefore totals 45. If you know the sum of some cells in one of those units, subtract it from 45 to find the sum of the remaining cells.

A worked example

Suppose several complete cages lie entirely inside one box. Together they cover eight of its nine cells and their labels add up to 39. The remaining cell must be 45 − 39 = 6.

If two cells remain instead, the subtraction gives their combined total, not an individual answer. You still need the row, column, box or cage constraints to separate the two digits.

Cages that cross the box boundary

Do not add a crossing cage's entire label to a box total: the label also includes cells outside that box. Either use complete cages contained in the box, or account explicitly for the outside cells.

For example, imagine a group of complete cages covers all nine cells of a box plus one cell outside it. If those cages total 51, the outside cell is 51 − 45 = 6. This works because the cells you counted are precisely one full box and one extra cell.

Killer Sudoku Cheat Sheet

Use this quick reference beside today's daily killer sudoku. All combinations below use distinct digits; you must still work out their positions.

How to Solve Your First Killer Sudoku

1. Scan for extreme totals. Start with two cells totalling 3 or 17, or three cells totalling 6 or 24. Write down the forced sets.
2. Keep candidates when the order is unclear. Use Notes for a cell you are actively considering rather than placing a guess.
3. Cross-check each cell. Remove digits already present in its row, column and box. If only one remains, enter it.
4. Check the rule of 45. Look for a row, column or box whose known sums leave only a small gap.
5. Rescan after every placement. A new digit can narrow a neighbouring cage or create another cell with a single candidate.

When one area stops giving you information, try another. A cage can be partly understood without being finished. Return to it after a nearby placement changes its candidates.

Killer Sudoku Tips for Beginners

Separate the two questions: “Which digits are in this cage?” and “Where can each digit go?” A sum can answer the first while leaving the second open. Keep both in mind when deciding what to enter.

On 1geplay, Notes keeps candidates visible, Check highlights conflicts and incorrect entries, and Hint supplies a correct digit. Check does not change your entries. Try tracing a highlighted contradiction before asking for a hint.

Leave the puzzle when you need a break. Your progress is saved in this browser when storage is available; there is no countdown forcing a quick answer.

Common Mistakes to Avoid

Matching the total but repeating a digit

2 + 2 reaches 4, but it breaks the cage rule. Check both the sum and the no-repeat restriction, then check the row, column and box.

Treating a combination as a fixed order

A cage containing 1 and 2 might be arranged either way. The total alone cannot choose their cells. Use the other constraints before placing them.

Counting a crossing cage as part of one box

A cage label includes all its cells, including those outside your chosen unit. Only subtract sums that account for the cells you actually mean to count.

Frequently Asked Questions

Do I need to know normal sudoku first?

No, but understanding rows, columns and 3×3 boxes makes the cage clues easier to use. You can learn all four constraints together using the rules above.

Can I guess or trial-fill?

You can, but an unsupported entry can create misleading clues elsewhere. Keep uncertain digits in Notes so you can distinguish a possibility from a deduction.

When does the daily puzzle change?

1geplay uses your device's local date. Open or reload the page after midnight to get the new day's grid. Reloading during the same date keeps the same puzzle.

How is killer sudoku different from sudoku?

Both use the same row, column and box rules. Killer Sudoku adds cages with totals and a separate no-repeat rule inside each cage. Those totals can replace the filled-in starting digits you expect in ordinary sudoku.

Is killer sudoku harder than sudoku?

It depends on the grid. Clear cage totals can give you an immediate starting point; ambiguous totals and deductions spread across several units can take more work. The extra arithmetic does not automatically make every Killer Sudoku harder.