What is Killer Sudoku?

Killer Sudoku combines Sudoku with simple arithmetic. It uses the normal 9×9 rules plus dotted "cages" of cells that must add up to a target sum.

What do the dotted cages and small numbers mean?

The dashed outline groups cells into a cage, and the small number in its corner is the total those cells must add up to.

Can a digit repeat inside a cage?

No. Besides the usual row, column and box rules, a digit cannot repeat within a single cage.

Does Killer Sudoku have starting numbers?

Usually not. Killer puzzles often start with an empty grid and are solved purely from the cage sums and Sudoku rules.

What is the 45 rule in Killer Sudoku?

Each row, column and 3×3 box always sums to 45 (1+2+…+9). Comparing that total to the cages that cover a region lets you deduce missing values.

How do you play Killer Sudoku?

Start with cages whose sum has only one possible combination — a 2-cell cage of 3 can only be 1+2, a 3-cell cage of 24 can only be 7+8+9. Pencil those in, then use the 45 rule on rows, columns and boxes that cages nearly cover. Once digits start landing, solve the rest like Classic Sudoku.

How many killer cage combinations are there?

There are 502 in total across cage sizes of 2 to 9 cells. The most valuable are the sums with only one possible combination, because they give you a cage outright.

Killer Sudoku

A Killer Sudoku board starts empty — the dashed cages and their target sums are the only clues. The "3" cage can only be 1+2, and the "17" can only be 8+9.

Killer Sudoku combines Classic logic with light arithmetic. The standard rules still apply (1–9 in every row, column and box), but there are no given numbers.

Killer Sudoku rules

The grid is split into dashed-outlined cages. Each cage shows a small target sum in its corner. Three rules, and that is the entire game:

Every row, column and 3×3 box contains the digits 1–9 exactly once — the Classic rules, unchanged.
The digits inside a cage must add up to its target sum.
A digit can never repeat inside a cage, even if the cage spans two boxes.

That third rule is the one beginners forget, and it is the most useful of the three: it means a cage is a set of distinct digits, which is what makes the sums predictable at all.

How to play Killer Sudoku, step by step

Find the forced cages first. Some sums have only one possible set of digits — a 2-cell cage of 3 can only be 1+2, a 3-cell cage of 24 can only be 7+8+9. Pencil those in immediately; they are free information.
Use the rule of 45. Every row, column and box holds the digits 1–9, so it sums to 45. If cages cover a box completely except for one cell, that cell is 45 minus the cage totals — a placement with no guesswork at all. See the rule of 45.
Look at cages that stick out. When a cage pokes one cell outside a box, the difference between the cage total and 45 tells you that cell's value — the innies and outies technique.
Then solve it like Classic. Once digits start landing, singles and pairs do the rest. Killer is Classic Sudoku with a head start, not a different puzzle.

The combinations are the whole game

Killer solving lives or dies on knowing which digits can make a given sum. There are 502 possible cage combinations in total, and the ones with a single answer are worth memorising — they hand you a cage outright.

We keep the full lookup as a separate page: the complete killer combinations reference, with every cage size from 2 to 9 cells and the unique sums highlighted. Keep it open in a second tab while you play.

Built-in helper

Select any cell and SudokuStreak highlights its whole cage and shows a live “Cage [target] — [left] to go” readout — the cage’s target sum and how much is still missing, so you always know what you’re aiming for. It does the addition; the deduction is still yours.

Common mistakes

Repeating a digit inside a cage. Legal for the row, illegal for the cage. A cage spanning two boxes still cannot hold two 5s.
Doing arithmetic instead of logic. Adding up is the easy half. The solving happens when you ask which combinations a sum allows, then eliminate the ones the grid forbids.
Ignoring the big cages. A 5-cell cage looks unhelpful, but extreme totals are just as forced as small ones — a 5-cell cage of 15 can only be 1+2+3+4+5.

Best techniques for Killer Sudoku

These are the solving techniques that pay off most in Killer Sudoku — each links to a full, illustrated guide.

Key Crosshatching Still the fastest opening move once a few cage digits are placed. → Key Naked Single Still essential in Killer: once cage sums pin a few digits, naked singles clear the rest. → Key Hidden Single in Sudoku Works exactly as in Classic; cage restrictions often force a digit into a single cell. → Key Naked Pair Cage combinations frequently produce naked pairs — a natural next step after the sums. → Key Hidden Pair in Sudoku Cage combinations restrict where digits can sit, which often forces a hidden pair. → Key Naked Triple Common in Killer, where cage sums frequently pin three cells to three digits. → Key Pointing Pairs in Sudoku (Locked Candidates) Cage sums restrict candidates to a line inside a box surprisingly often. → Key Box/Line Reduction in Sudoku (Claiming) Common in Killer once cage arithmetic pins a digit to one box of a line. → Useful Snyder Notation Helps, though Killer solvers usually need full cage-candidate marks too. → Key The Rule of 45 in Killer Sudoku The single most important Killer technique — the foundation everything else builds on. → Key Killer Combinations You reach for these combinations on almost every cage. → Key Full House Cage sums often fill a unit to all-but-one, handing you a full house. → Key Innies and Outies The workhorse for cracking a Killer grid once the rule of 45 alone stalls. → Useful Hidden Triple in Sudoku Appears, though cage arithmetic usually gets there first in Killer. → Useful Naked Quad Occurs where cage sums restrict four cells to four digits. → Key Cage Splitting A staple once single innies and outies run out. → Key Cage/Unit Overlap Blends intersection logic with cages — very handy in Killer. → Useful X-Wing Sudoku Technique Explained Works, but Killer's cage sums usually crack the grid before an X-Wing is needed. → Useful XY-Wing Sudoku Technique (Y-Wing) Explained Useful, though cage arithmetic usually resolves Killer before wings are needed. → Useful Turbot Fish Works once candidates settle, though cage logic usually resolves Killer sooner. → Useful X-Cycles Occasionally needed once cage arithmetic stalls on a stubborn digit. → Useful 3D Medusa Useful late, though cages usually break the grid before Medusa is needed. → Useful Unique Rectangle Applies, but Killer's cage constraints usually settle things another way first. → Useful Forcing Chains Rarely needed — cage arithmetic usually resolves Killer before chains become necessary. → Useful Aligned Pair Exclusion Cage almost-locked sets give it plenty of forbidden combinations to exploit. → Useful ALS-XZ Killer cages naturally form almost locked sets, so ALS logic is at home here. → Useful Death Blossom Cages supply ready-made petals, making the pattern natural in Killer. → Useful Alternating Inference Chains (AIC) Useful once cage arithmetic stalls, linking candidates across the grid. → Useful ALS-XY-Wing Cages provide ready almost locked sets to chain into a wing. → Useful Grouped Chains Useful once cage arithmetic stalls, with groups adding extra links. →

Difficulties & scoring

This type can be played on all five difficulties. The score multiplier for Killer Sudoku is ×1.3 — so every point counts for more on this variant. The "normal time" below is tuned for this type.

Difficulty	Base score	Max (×1.3)	Normal time	Hints
easy	150	390	7 min	6
medium	300	780	14 min	5
hard	600	1560	21 min	4
expert	1000	2600	28 min	3
evil	1500	3900	42 min	2

How the score is calculated

Your score builds up from 0 as you place correct numbers, up to the full base when the board is finished. Then two bonuses are added:

base × your progress × (1 + combo bonus + time bonus) × 1.3

Progress: the live score climbs from 0 to the base as the grid fills with correct numbers.
Combo bonus (up to +50%): keep a clean run for the full bonus. Each error or hint is a combo break that shrinks the bonus — but it never takes Sparks away below the base.
Time bonus (up to +50%): beat the normal time and you earn extra, proportional to how much faster you were. Finishing slower than normal costs nothing — there is no time penalty.
The total is multiplied by ×1.3 and never drops below 0.

Coins

The coins you earn reflect your score — the more Sparks, the more coins (about 1 coin for every 45 Sparks, minimum 1). Spend coins in the Shop on hints and Jokers.

Tip: a clean, hint-free solve under the normal time scores the highest. The Daily Challenge is always Classic and fully scored.