Learn how Locked Candidates work in Sudoku, including the Pointing and Claiming techniques. These essential intermediate strategies help eliminate candidates and create progress in tougher puzzles.

Sudoku Tips: Locked Candidates Explained (Pointing & Claiming)

Most Sudoku players eventually run into the same problem.

The easy singles disappear, obvious eliminations stop working, and the puzzle suddenly feels much harder than it did a few minutes earlier.

At that stage, solving becomes less about individual cells and more about understanding how different parts of the grid interact.

One of the most useful techniques for this transition is Locked Candidates.

This strategy appears frequently in intermediate and expert puzzles because it creates eliminations by connecting rows, columns, and boxes together.

What Are Locked Candidates?

Locked Candidates occur when the possible positions for a number become restricted within a row, column, or 3×3 box.

Once that restriction exists, certain candidates elsewhere in the grid can no longer be valid.

There are two forms of the technique:

Pointing
Claiming

Although they are usually taught separately, both rely on the same core principle:

If a candidate is forced into a specific area, it can often be removed from somewhere else.

Pointing

How Pointing Works

Pointing occurs inside a 3×3 box.

If all possible positions for a candidate within that box lie in the same row or column, the candidate becomes “locked” into that line.

Because of that, the same candidate can be eliminated from the rest of the row or column outside the box.

Pointing Example

Suppose candidate 4 appears only twice inside a box.

Both candidate 4s are located in the same row.

That means the final placement for 4 in that box must occur somewhere along that row.

As a result:

Any other candidate 4s elsewhere in the same row
Outside the box
Can be removed

The box effectively “points” into the row.

Why Pointing Matters

Pointing is important because it creates eliminations that are easy to miss during normal scanning.

Many puzzles become solvable again after just one clean pointing elimination.

It is also one of the first techniques that teaches players to think beyond isolated cells.

Claiming

How Claiming Works

Claiming works in the opposite direction.

Instead of starting from a box, it begins with a row or column.

If all possible positions for a candidate in a row are confined to a single box, then that candidate must ultimately be placed somewhere inside that box.

Therefore:

The same candidate can be removed from other cells within the box

Claiming Example

Imagine candidate 7 appears only twice in a row.

Both candidates happen to fall inside the same 3×3 box.

Since the row must place its 7 somewhere inside that box, any other candidate 7s within the box become impossible.

Those candidates can be eliminated safely.

In this case, the row is effectively “claiming” part of the box.

Pointing vs Claiming

These two patterns are closely related, but the direction of elimination is different.

Technique	Starting Area	Elimination Area
Pointing	Box	Row or column
Claiming	Row or column	Box

A useful way to remember them:

Pointing pushes outward from a box
Claiming pulls inward into a box

How to Spot Locked Candidates

The most effective approach is to scan candidate-by-candidate rather than cell-by-cell.

Choose a number and follow its positions carefully across the grid.

Look for situations where:

A box restricts a candidate to one line
A line restricts a candidate to one box

These patterns become much easier to recognize once pencil marks are organized clearly.

Experienced solvers often identify Locked Candidates almost automatically while scanning.

Common Mistakes

Removing Candidates Too Early

The restriction must be complete.

If a candidate still appears elsewhere in the box, row, or column, the pattern is invalid.

Confusing Pointing and Claiming

The underlying logic is similar, but the elimination direction changes.

Understanding where the restriction begins is more important than memorizing the names.

Ignoring Partial Information

Locked Candidates often appear before the board looks “advanced.”

Many players miss them simply because they stop scanning too soon.

When Should You Use Locked Candidates?

Locked Candidates usually become useful once basic singles and pairs begin slowing down.

They appear frequently in:

Medium difficulty puzzles
Hard classic Sudoku
Candidate-heavy late-game situations

In many cases, a single Locked Candidate elimination is enough to restart progress across the grid.

Developing Better Pattern Recognition

Like most intermediate Sudoku techniques, Locked Candidates are less about calculation and more about recognition.

Strong players are constantly watching how candidates cluster together.

Over time, these interactions become easier to notice naturally.

The important thing is not speed.

It is learning to read the structure of the puzzle accurately.

Final Thoughts

Locked Candidates are one of the most practical techniques in Sudoku because they appear often and produce reliable eliminations without requiring advanced chain logic.

For many players, this is the point where Sudoku starts becoming more strategic and far less dependent on trial-and-error.

Once you become comfortable with Pointing and Claiming, the entire grid begins to feel more connected — and difficult puzzles become much easier to control.