Play Today's Killer Sudoku Daily Puzzle

How to Play Killer Sudoku

Modes: Easy · Medium · Hard · Daily

Killer Sudoku follows all the classic Sudoku rules: every row, column and 3×3 box must contain the numbers 1 to 9 exactly once.

The board is divided into dashed cages. Each cage shows a small number — the digits inside that cage must add up to exactly that total.

A cage with a single cell is simply a given digit: that number is filled in for you.

Select a cell and tap a number to place it, or switch on Notes to pencil candidate digits. Erase clears the selected cell.

Rules

Every row, column and 3×3 box holds 1–9 with no repeats.

All cells in a cage must sum to the cage’s target number.

Digits may repeat within a cage as long as they are in different rows, columns and boxes.

The puzzle is solved when every row, column, box and cage constraint is satisfied.

Scoring

History & Origins of Killer Sudoku

Killer Sudoku was invented in 2005 for The Times in London by Wayne Gould, and it exploded around the world within a few years. The idea was simple to sell: take classic Sudoku, remove many of the given digits, and replace them with dashed cages whose small corner totals must be reached by the digits inside. Adding those sums back onto the solving process gave newspapers a fresh daily format to champion.

Where a standard Sudoku hands you fixed clues, Killer Sudoku hides the digits behind arithmetic. Because every row, column and 3x3 box adds up to 45, a cage that pokes across a boundary gives away the part that lies outside it, and solvers quickly learn to lean on those running totals. A single-cell cage is simply a given digit in disguise.

The appeal is that the Sudoku skeleton never disappears: rows, columns and boxes still forbid repeats, and the cages simply add a layer of sums on top. ThinkyPlay controls difficulty through how many single-cell givens appear in the starting grid, from a comfortable handful on Easy down to almost none on Hard. Every board is verified to have exactly one solution before it reaches you.

That blend of counting and classic placement is what made the format stick where other Sudoku variants faded. The cage totals reward quick mental arithmetic and a feel for the common digit combinations, while the underlying grid keeps the reassuring row, column and box logic of the puzzle everyone already knows.

Common Mistakes to Avoid

• Duplicating a digit inside a cage that crosses two 3x3 boxes, forgetting that the cage total never overrides the Sudoku ban on repeats.
• Treating a single-cell cage as editable, when in fact it is a given digit that locks that value permanently.
• Filling a cage to its exact target while ignoring the row, column and box constraints, so the completed cage sits inside a broken Sudoku line.
• Piling digits into a cage until the running sum already overshoots the target, instead of reading the red warning as a cue to backtrack early.

Tips & Strategy

Start with 1-cell cages — they are givens. Then look for 2-cell cages with small or large totals: 3 must be 1+2, and 17 must be 8+9.

Sum whole rows, columns and boxes: each totals 45, so a cage that crosses a boundary lets you deduce the remainder.

Remember that 45 minus a cage total shows what is missing from that row, column or box.

Use pencil notes to track the few candidates each cage allows.

The Hint button reveals one correct digit when you are stuck.

Frequently Asked Questions

Is Killer Sudoku free to play?

Yes — Killer Sudoku on ThinkyPlay is completely free, with no download and no sign-up.

What is the difference between Sudoku and Killer Sudoku?

Killer Sudoku adds cages: the digits in each dashed cage must add up to its target total. This replaces many given digits with sums to deduce.

Can digits repeat inside a cage?

Yes — as long as the Sudoku row, column and box rules are respected, a cage may repeat a digit (for example a 2-cell cage of 2 could be 1+1 only if the cells do not share a row, column or box).

Why does 45 matter in Killer Sudoku?

Every row, column and box sums to 45. Cages that straddle these boundaries reveal the part that sits outside, which is often the fastest way to place a digit.

Why is a one-cell cage already filled in?

A single-cell cage is a given: the digit shown is fixed and locked, exactly like a clue in classic Sudoku. Treat it as solved and build your cage sums around it.

What changes between Easy, Medium and Hard?

Easy boards open with roughly eight to fourteen locked single-cell digits; Medium trims that toward four to nine; and Hard can start with just one to seven givens while cages grow longer, leaving almost everything to the sums.

What do the red highlights flag in Killer Sudoku?

Red marks a digit that repeats in its row, column or box, or a cage whose filled digits already overshoot the target or finish on the wrong total once complete.