Medium 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
6
17
19
23
5
7
16
2
12
13
11
21
7
19
14
8
25
29
13
14
31
22
10
7
27
3
13
11
Try Hard →
Progress0%
28 cages All Killer →
How to play Killer Sudoku
The board starts with pre-filled digits as clues. 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}

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.

Medium tip - After placing forced cages, apply the 45 rule row-by-row and column-by-column. Look for innies and outies whenever a cage crosses a box boundary - They often reveal a cell value without needing candidates at all.

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 is Killer Sudoku?

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

Solving Techniques for Medium 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

Master these, then take on Hard Killer Sudoku to learn Advanced techniques.

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 — Medium Killer Sudoku

What techniques do I need for medium Killer Sudoku?
Medium puzzles require combining cage sum elimination with the 45 Rule across rows, columns, and boxes. You'll need naked pairs and hidden singles, plus innie/outie analysis where cage totals leave a known single-cell remainder in a unit. Pencil marks become important at this level.
How do innies and outies work?
An innie is a cage cell that sits inside a unit (row, column, or box) while the rest of its cage is outside — its value equals 45 minus the total of all cages fully inside the unit. An outie is the reverse. At medium difficulty you'll encounter 1-cell innies and outies regularly; they give direct digit placements without any combination enumeration.
How long does medium Killer Sudoku take?
Most players finish a medium Killer Sudoku in 20–40 minutes. If you're new to the 45 Rule, expect longer until it becomes instinctive. The technique scales well — once you can apply it quickly to every unit, medium puzzles resolve with satisfying speed.
Can I solve medium Killer Sudoku without the 45 Rule?
You can sometimes get partway using only cage combinations, but medium puzzles are specifically designed to require innie/outie analysis for key deductions. Without the 45 Rule you'll almost certainly hit a dead end. It's worth spending time on easy puzzles to make the 45 Rule automatic before tackling medium.
What is the hardest deduction at medium Killer Sudoku?
Multi-unit innies and outies — where a leftover cage cell is shared between two units (e.g. a box and a row) — are the trickiest medium deductions. The cell must satisfy the innie/outie calculation for both units simultaneously, often pinning it to a single digit that cage enumeration alone would never reach.

More questions? See the full Killer Sudoku FAQ.