Expert Killer Sudoku

Easy Medium Hard Expert
Mistakes
0/3
Score
-
Time
00:00
26
5
23
7
8
12
15
11
4
13
20
27
18
4
18
29
18
3
24
7
20
8
8
22
19
15
3
4
11
3
New Game
Progress0%
30 cages All Killer →
How to play Killer Sudoku
The board starts empty - There are no given digits. Your clues are the cage sums (small numbers in cell corners). Fill each cage so the digits sum to that total, with no repeats within any cage. All standard Sudoku rules still apply (1–9 in every row, column and 3×3 box).

Killer Sudoku - Complete Guide

Difficulty Overview
LevelGiven digitsCagesAvg. solve time
Easy~26~28–325–10 min
Medium~18~30–3610–20 min
Hard~8~34–4020–40 min
Expert0~36–4540–90 min
Cage Sum Limits
Cage sizeMin sumMax sumForced?
1 cell19Yes (unique)
2 cells317At extremes
3 cells624At extremes
4 cells1030At extremes
5 cells1535At extremes
9 cellsAlways 45Yes

Forced cage combinations you must memorise

2-Cell cages - Forced sets
SumOnly possible set
3{1, 2}
4{1, 3}
16{7, 9}
17{8, 9}
3-Cell cages - Forced sets
SumOnly possible set
6{1, 2, 3}
7{1, 2, 4}
23{6, 8, 9}
24{7, 8, 9}

Key solving techniques

45 Rule
Every row, column, and 3×3 box sums to 45. If all cages in a row are known except one cell, the missing value = 45 − (sum of all other cage totals in that row). This is the single most powerful Killer technique.
Innies and Outies
When a cage partially straddles a row/column/box boundary, the cells inside the boundary are "innies" and those outside are "outies." Their sum difference reveals exact values using the 45 rule, often resolving cells without any candidates.
Cage Elimination
No digit may repeat within a cage. List all combinations that produce the cage sum, then cross-eliminate those that conflict with placed digits in the same row, column, or box. Often narrows a cage to a single combination early in the solve.
Naked Subsets in Cages
When two cells in a cage can only hold two specific digits (a naked pair), those digits are locked into that cage and can be eliminated from the rest of their shared row, column, or box - Exactly like standard Sudoku naked pairs.

Difficulty comparison - Constraint density

Higher constraint density = fewer given digits but more cage interactions per cell on average.

Easy 32%
Medium 52%
Hard 72%
Expert 100%

Frequently asked questions

Can a digit repeat inside a cage? +
No. Each digit must appear at most once within any cage, in addition to not repeating in its row, column, or 3×3 box. This is the core extra constraint of Killer Sudoku.
Do I need to do arithmetic to solve it? +
Basic addition is required. You need to figure out which digit combinations produce each cage sum. No multiplication or complex maths - Just 1–9 addition. Memorising the forced 2- and 3-cell combinations above covers the most common cases.
What does sharing a puzzle do? +
The Share button copies a URL containing the puzzle ID. Anyone who opens that link will see the exact same cage layout you are solving - Useful for competing with friends or comparing solve times on the same puzzle.
How is the score calculated? +
Score = max(0, 10 000 − time×10 − mistakes×200 − hints×500). Finishing faster with no mistakes and no hints gives the highest possible score of 10 000.
Explore More Sudoku Variants
Diagonal Sudoku Hyper Sudoku Odd/Even Sudoku Anti-Knight Anti-King Irregular Sudoku Classic Sudoku

Killer Sudoku - Complete Guide

Difficulty Overview
Level Given digits Cages Avg. solve time
Easy ~26 ~28-32 5-10 min
Medium ~18 ~30-36 10-20 min
Hard ~8 ~34-40 20-40 min
Expert 0 ~36-45 40-90 min
Cage Sum Limits
Cage size Min sum Max sum Forced?
1 cell 1 9 Yes (unique)
2 cells 3 17 At extremes
3 cells 6 24 At extremes
4 cells 10 30 At extremes
5 cells 15 35 At extremes
9 cells Always 45 Yes

Forced cage combinations you must memorise

2-Cell cages - Forced sets
Sum Only possible set
3 {1, 2}
4 {1, 3}
16 {7, 9}
17 {8, 9}
3-Cell cages - Forced sets
Sum Only possible set
6 {1, 2, 3}
7 {1, 2, 4}
23 {6, 8, 9}
24 {7, 8, 9}
4-Cell cages - Forced sets
Sum Only possible set
10 {1, 2, 3, 4}
11 {1, 2, 3, 5}
29 {5, 7, 8, 9}
30 {6, 7, 8, 9}
5-Cell cages - Forced sets
Sum Only possible set
15 {1, 2, 3, 4, 5}
16 {1, 2, 3, 4, 6}
34 {4, 6, 7, 8, 9}
35 {5, 6, 7, 8, 9}

Key solving techniques

45 Rule

Every row, column, and 3x3 box sums to 45. If all cages in a row are known except one cell, the missing value = 45 - (sum of all other cage totals in that row). This is the single most powerful Killer technique.

Innies and Outies

When a cage partially straddles a row/column/box boundary, the cells inside the boundary are "innies" and those outside are "outies." Their sum difference reveals exact values using the 45 rule, often resolving cells without any candidates.

Cage Overlap Counting

When a cage spans two boxes or rows, use subset counting to pin down which digits appear in the overlap region. Subtract partial cage sums to isolate individual cell values - Especially useful when the 45 rule leaves two unknowns.

Naked Subsets in Cages

If a group of cages within a unit accounts for exactly n cells using n digits, those digits are locked to those cells and removed from all other unit cells. Identical to classic naked pairs/triples but applied across cage boundaries.

Expert tip - With zero given digits, the 45 rule is your only entry point. Chain innie/outie deductions across multiple units before placing a single digit. Cage overlap counting and naked subsets will be required - Expect to maintain a full candidate grid from the start.

Frequently Asked Questions

Can digits repeat in a cage?
No - Every cage follows the no-repeat rule. Each digit appears at most once within any single cage.
What is the 45 rule?
Every row, column, and 3x3 box contains digits 1-9, summing to 45. Subtracting known cage sums within any unit reveals leftover cell values.
Is Killer Sudoku harder than Classic?
Generally yes - There are no given digits, so you rely entirely on cage arithmetic and elimination. Easy Killer is roughly equivalent to Medium Classic.
What are innies and outies?
When a cage crosses a unit boundary (row, column, or box), the cells inside that unit are called innies and those outside are outies. The sum difference between them and 45 reveals exact cell values.
Do I need to guess in Expert Killer?
A well-formed Expert puzzle is always logically solvable - No guessing needed. However, the required deduction chains are long and involve cage overlaps and naked subsets across the full grid.