10 Sudoku Tips for Beginners, According to Experts

Whether you’re a total beginner with no clue at all as to how to solve Sudoku or an experienced player in search of Sudoku tips and tricks to get you to the next level, you’re in luck. The brain game–obsessed crew over here at Reader’s Digest spoke with Simon Anthony and Mark Goodliffe, two of the U.K.’s most dedicated puzzlers, who have represented the United Kingdom multiple times at the World Sudoku Championships. And you don’t get that far in the world of competitive Sudoku without an arsenal of no-fail Sudoku strategies at the ready.

First and foremost, you need to know that Sudoku is a logic puzzle that rewards deductive reasoning. Of course, if you’ve never played before, that may not mean all that much just yet. But no worries—before launching into Anthony and Goodliffe’s Sudoku tips, we’ll cover the basics of how to solve Sudoku and what the game is really all about.

Read to find out all there is to know about solving Sudoku like an absolute pro.

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What Sudoku is

Sudoku is a numbers puzzle, although it’s not a math puzzle, per se. In fact, a classic Sudoku grid requires no computation, except in the case of a Sudoku-based game called Killer Sudoku, which we’ll address later. You might even consider Sudoku to be a visual puzzle because it calls upon your ability to recognize patterns.

The correct way to play Sudoku

Sudoku began its journey to brain game fame in 1979—long before screens became ubiquitous. So how did people play Sudoku back then? They used a pencil and paper.

That said, Sudoku is also delightfully screen-friendly. Beginners may even prefer playing on a phone or computer for reasons we’ll get into later on.

Every Sudoku puzzle consists of a two-dimensional grid of nine rows and nine columns—essentially a nine-by-nine spreadsheet with 81 spaces, often called “cells.” In addition, the Sudoku grid is divided into nine three-by-three squares (also known as boxes), each comprising nine cells. The goal is to fill all 81 cells with a number from one through nine, subject to two caveats:

• No number may appear more than once in any “house,” meaning a row, column or square.
• Each game begins with some of the 81 cells already filled in. These “givens” actually provide all the information you need to solve the puzzle.

So the general rule is that the fewer the given numbers, the more challenging the grid will be. Just like Rebus puzzles, you need patience, logic and a sharp eye to solve a Sudoku.

Sudoku glossary

The best Sudoku tips for solving any puzzle

Unlike Wordle and Connections, Sudoku puzzles tend to come labeled by their degree of difficulty. Some could be so easy that you solve them in minutes, while others could take you days of pondering! Regardless of how easy or hard the puzzle is, all must be solved in the same way; that is, through the process of elimination.

Any blank cell could, in theory, contain any of the digits from one to nine. Sudoku gameplay consists of eliminating wrong numbers until only the right ones remain.

What follows is the best way to go about it and some handy Sudoku-solving techniques.

Understand the “candidates”

In Sudoku parlance, every digit (one through nine) that could be slotted into a cell on a grid is known as a candidate.

• If a digit already appears elsewhere in a blank cell’s row, column or square, then it cannot be a candidate for that particular blank cell.
• In other words, when considering a blank cell, if a digit already exists elsewhere in its house, then it is not a candidate.

Avoid “automatic candidates”

A Sudoku tip that Anthony and Goodliffe recommend is to avoid “automatic candidates,” a setting in many on-screen iterations of Sudoku that allows you to make all candidates visible with a single click.

As tempting as that may seem, the downside is that it can be difficult to see even simple patterns within the Sudoku grid when every cell has lots and lots of markings in it.

Don’t guess

There are many worthy Sudoku strategies to help you fill out the grid, but guessing is not one of them. As Anthony and Goodliffe put it, “Guessing avoids finding the logic that most Sudoku puzzles inherently possess, and therefore, you neither maximize your chance of finding the solution nor improve your skills.”

Consider these your “rules” of the game:

• A legitimate or fair Sudoku grid should require no guessing at all, and our experts advise steering clear of any grids that do.
• Sudokus found in newspapers and magazines, along with many you’ll find online, tend to be fair.
• Don’t glance at the solutions. Puzzles are excellent for your cognition, but only if you solve them yourself.

Seek out the obvious ones first

Most Sudoku grids will come with some number of blank cells for which, thanks to the placement of givens, only one candidate is possible. Because every cell you fill in offers new information about the remaining empty cells, Anthony and Goodliffe recommend this as the first Sudoku-solving technique: Seek out this “low-hanging fruit” in the rows, columns and squares that contain the greatest number of givens.

• The harder the puzzle, the fewer of these you will find. However, if they’re there, it’s by design, and a good scan of a fresh grid should reveal them.
• Fill in these obvious candidates as a stepping stone to solving the rest of this intriguing logic puzzle.

Take the “square route”

No, the square route isn’t a math trick that Sudoku-solving requires. It’s one of the most popular Sudoku tips: Focus specifically on what our expert duo refers to as “chutes” of three adjacent nine-by-nine squares. These occur both vertically and horizontally.

The rule of thumb, which some people refer to as the three-number rule, is that “a digit must appear three times per chute but only once per row, column and box.”

• Begin by scanning for rows or columns within the chute that already have two of the same digit. This will hone it down to a single row or column where the third occurrence of that digit fits.
• Often, there will be only one particular cell where the third instance of that digit can go; if so, you’re now one step closer to solving the puzzle overall. Other times, however, there may be two or three cells where a digit could go.

And this is where the next Sudoku strategy comes in.

Make use of “pencil-marking”

Once you have identified a number that can fit into two or even three possible cells in one house, it’s time to break out the pencil-marking strategy, which Anthony and Goodliffe tell us was first popularized by three-time World Sudoku Champion Thomas Snyder.

Here’s how this Sudoku tip works:

• If there’s one digit that can go in exactly two cells in one square, put a little “pencil mark” (or otherwise note the digit is a candidate) in the corner of each of those two cells.
• Fill in more of the cells. It should eventually become obvious which of these cells is the correct one for a certain digit.
• When you land on the correct cell for the digit, either circle the digit or erase the small candidates in the corner and write the digit larger in the center of the cell.

When playing Sudoku online, you won’t need an actual pencil; most online iterations of the game allow you to work in pencil-marking mode, although they may call it something else, such as Notes or Candidates mode.

The pencil-marking strategy is so effective that once you master it, our experts say you’ll be able to solve virtually any Sudoku puzzle—even the most difficult. Even better, pencil marking will help you finish faster.

Find and make use of “hidden pairs” and “hidden triples”

Once you’ve mastered pencil marking, you can move on to important Sudoku strategies known as “hidden pairs” and “hidden triples.”

A hidden pair refers to two candidates that appear in two cells in the same house and nowhere else in the house (remember, a house is any of a single row, column or square) where at least one of the two cells has other candidates.

Those other candidates can be summarily eliminated—without another thought. Here’s why: Of those two candidates, one is the solution to one of those two cells, and the other candidate is the solution for the other cell. Therefore, the unpaired candidates in those two cells cannot possibly be the solution to either.

Using hidden triples works the same way except that there have to be three cells in which the same three candidates appear, and those same three candidates cannot appear in any other cell.

Give the X-Wing technique a go

The X-Wing is arguably the simplest of all advanced techniques, although there’s really nothing simple about it. It refers to a scenario in which:

• One candidate occurs in two cells in each of two rows.
• Those two cells are also located in the same two columns.

As long as there are no other cells for which the digit in question is a candidate, you’ll be able to eliminate all other candidates in all four of the cells thanks to this Sudoku-solving technique. And that, of course, can be very useful.

Try to solve Killer Sudoku

In every Sudoku grid, if you were to add up all the numbers in any given house, the sum would always be 45. This is known as the 45 rule, according to Anthony and Goodliffe, and it forms the basis of Killer Sudoku, a separate game that derives from classic Sudoku. It’s also the only Sudoku context in which computation plays a role, making it a math puzzle of sorts.

You’ll immediately recognize a Killer Sudoku grid because:

• There are no givens.
• The empty puzzle includes bracketed groupings of blank cells, each with a number that the grouping of cells will have to add up to.

Your job as a player is to figure out which numbers between one and nine go into which cells such that the bracketed groupings add up to what they’re supposed to and no digit appears more than once in a house.

Of course, if you came to Sudoku for the not-math of it all, feel free to regard the 45 rule as nothing more than a fun fact!

Practice and practice some more

If you’re a beginning Sudoku player looking to improve your game, there’s no substitute for practice, say Anthony and Goodliffe. Not only will you get better at recognizing patterns within your pencil markings, but you’ll also be better equipped to use some of the more advanced Sudoku tips and tricks.

FAQs

What are some common mistakes beginners should avoid when solving Sudoku?

Common mistakes include guessing the numbers without answering why they should be there in the first place. Allowing duplicate candidates—that is, entering the same number in the row, column or square—is another newbie mishap. This could lead to the entire Sudoku being solved incorrectly. So be careful!

How can I improve my speed when solving Sudoku puzzles?

Practice again and again. Think of a Sudoku like a jigsaw puzzle that you will get better at solving with every try. If you feel you’re getting stuck, take a break and revisit the puzzle. Use our expert-recommended Sudoku tips to solve Sudoku puzzles quickly and easily.

What is the three-number rule in Sudoku?

The three-number rule, also known as the rule of thumb, is that a digit must appear three times per chute but only once per row, column and box. Remember, a chute refers to any three adjacent nine-by-nine squares, whether vertically or horizontally.

What are some effective ways to keep track of possible numbers in each cell without getting overwhelmed?

Pencil-marking is a great technique to keep track of the candidates that are possible for each cell. You could simply make a small mark in the corner of the cell or even turn on pencil-marking mode in a digital Sudoku app. This helps you remember the logic and deduction you used, and ultimately makes it easier to fill in all the numbers and solve the puzzle.

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Sources:

• Simon Anthony and Mark Goodliffe, founders of Cracking the Cryptic; email interview, May 8, 2024
• Cornell University: “The Math Behind Sudoku”

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