Hard Sudoku

On a hard puzzle you will reach a point where no square has an obvious answer. From there you need notes: the possible numbers written into each empty square. With notes in place, patterns appear that let you rule numbers out until a square has only one option left.

The puzzle above opens on Hard. You can switch level at any time with the Difficulty buttons. Every puzzle is checked by a solver to make sure it has exactly one answer.

What hard sudoku asks of you

• Full notes. Write every possible number into every empty square. Do it number by number, it is quicker and you miss less.
• Naked pairs. Two squares in the same row, column or box with the same two notes, say 3 and 7. Those two numbers belong to those two squares, so remove 3 and 7 from every other square in that group.
• Hidden pairs. Two numbers that can only go in the same two squares of a group. Those squares must hold them, so their other notes can go.

Each of these is explained step by step in our Sudoku strategy guide. When notes start to matter, read when to use pencil marks.

At a glance

Starting numbers	About 31 of 81
Time	Typically 15 to 40 minutes.
Good for	Confident players who enjoy using notes and want a puzzle that needs a plan.
What next	When pairs feel natural, try Expert, which adds pointing pairs and box and line checks.

Other levels

Questions people ask

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