Expert Killer Sudoku

Cage sums meet classic Sudoku logic. Digits in each cage must total the clue — no repeats allowed. Free, no login required.

Easy Medium Hard Expert
Mistakes
0/3
Score
-
Time
00:00
1
27
13
16
19
12
6
3
12
9
13
5
17
17
7
6
1
21
9
17
8
18
20
4
27
9
17
7
16
9
21
18
All Killer Sudoku Puzzles →
Progress0%
32 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).
How to Play Killer 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.

What is Killer Sudoku?

Difficulty
★★★☆☆
3/5
Constraint Type
Cage Sums
Typical Givens
0 (all cages)
Avg. Solve (Expert)
70 min

Solving Techniques for Expert Level

Technique Description Level
Cage Sum Elimination Each cage has a fixed sum. Use the sum and the number of cells to calculate which digits are possible — e.g. a 2-cell cage summing to 3 can only be {1,2}. Beginner
No-Repeat Rule Digits cannot repeat within a cage. Combined with sum constraints, this eliminates many candidates immediately. Beginner
45 Rule Each row, column, and box sums to 45. Subtract known cage totals within a unit to find leftover cell sums — often isolating a single value. Intermediate
Innies and Outies An innie is a cage cell inside a unit whose sum reveals a digit; an outie is outside. These provide single-cell deductions without full candidate tracking. Intermediate
Cage Overlap Counting When a cage spans two boxes or rows, use subset counting to pin down which digits appear in the overlap cells. Advanced
Naked Subset 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. Advanced

Average Solve Time by Difficulty

Easy
8 min
Medium
18 min
Hard
38 min
Expert
70 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Killer Sudoku →

Frequently Asked Questions — Expert Killer Sudoku

Is expert Killer Sudoku the hardest level?
Expert Killer Sudoku is among the most demanding logic puzzles available. Every cage in the grid has many possible combinations, and only the most precise application of the 45 Rule, multi-cell innies/outies, and advanced Sudoku techniques — X-Wings, Swordfish, forcing chains — will break them open.
Can you solve expert Killer Sudoku without guessing?
Yes. Every expert puzzle on Sudoku.by has a unique logical solution provable without trial and error. Guessing leads to contradictions that are hard to untangle. The solution always follows from the 45 Rule, cage combination elimination, and advanced Sudoku deduction applied with full precision.
What advanced strategies appear in expert Killer Sudoku?
At expert level you need: extended 45 Rule across overlapping units, subset counting within cages spanning multiple boxes, naked and hidden subsets inside cages, and multi-unit forcing chains where a cage combination is eliminated because it produces a contradiction several steps later.
How many clues does an expert Killer Sudoku have?
Expert puzzles have no pre-filled digits inside the grid — all information comes from cage sums. Every cage has multiple valid combinations and none resolve immediately from sum arithmetic alone. The entire solve flows from the 45 Rule and advanced eliminations from start to finish.
How long does an expert Killer Sudoku take?
Expert puzzles take most players 60–90 minutes. Highly experienced solvers who apply the 45 Rule instinctively and recognise advanced patterns may finish in 45–65 minutes. If you're stuck for more than 20 minutes, revisit every unit with the 45 Rule — there is almost always an innie or outie you haven't yet exploited.

More questions? See the full Killer Sudoku FAQ.