The hardest cage-sum puzzles on the site. Expert Killer Sudoku has zero given digits, rare cage combinations, and interactions that span the entire grid. Only the sharpest minds need apply.
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.