How to Spell Numbers from 1 to 100 (+ Mistakes to Avoid)

Number spelling trips up more of our children than you’d guess.

Is it forty or fourty? Does twenty-one need a hyphen? These are tiny gaps, but they do have a tendency to show up on every test and every written assignment and it’s really frustrating to lose points over that.

Today, our tutors walk you through how to spell numbers from 1 to 100: the patterns, the exceptions, and the mistakes to catch early.

The Basics: Numbers 1 to 20

Before any rules or patterns, the first twenty number words need to be learned by heart. No shortcuts, no patterns yet, just twenty words.

Here they are in full:

• One (1), two (2), three (3), four (4), five (5), six (6), seven (7), eight (8), nine (9), ten (10)

• Eleven (11), twelve (12), thirteen (13), fourteen (14), fifteen (15), sixteen (16), seventeen (17), eighteen (18), nineteen (19), twenty (20)

The first ten are mostly straightforward, with one exception worth flagging. Eight doesn't follow an obvious spelling pattern, and in our experience, students often second-guess the order of the letters. It is one we recommend slowing down on.

From eleven onward, things get a little less predictable. The ones we see children trip over most often include:

• Eleven and twelve look nothing like the numbers they represent. There is no pattern to lean on, so these two simply need to be memorized.

• Thirteen through nineteen are more manageable. Most end in '-teen,' which connects them to the number they come from: four-teen, six-teen, seven-teen. The ones to watch are thirteen (not 'threeteen') and fifteen (not 'fiveteen'), as both shift slightly from what you might expect.

A little extra time on these goes a long way. Once twenty is solid, the spelling starts following a clear pattern, and everything from twenty-one onward becomes much easier to learn.

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How the Pattern Works from 21 to 100

This is where the spelling rules begin to make a bit more sense.

From 21 onward, number words are built in two parts: the tens word followed by the ones word, always joined by a hyphen. That's the rule, and it holds up all the way to ninety-nine.

The tens words your child needs to know are:

• Twenty (20), thirty (30), forty (40), fifty (50), sixty (60), seventy (70), eighty (80), ninety (90)

Notice anything? Most of them echo the ones words they come from:

• Six becomes sixty

• Seven becomes seventy

• Nine becomes ninety

That connection makes them easier to learn. 

Put the tens and ones together with any ones word (1-9), and you've got your number:

• Twenty + one = twenty-one (21)

• Forty + seven = forty-seven (47)

• Ninety + three = ninety-three (93)

The hyphen is not optional. It belongs there every time, whether the children are writing twenty-two or eighty-eight.

The round tens stand on their own with no hyphen needed, since there's no ones digit to attach. 

And at the very top of the range, one hundred follows the same logic: two clean words, no hyphen needed.

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Common Spelling Mistakes to Watch Out For

There are a handful of number words that regularly cause trouble, even for students who understand spelling patterns well. 

Here are the ones to watch:

• Fourty is wrong. The correct spelling is forty. The word four has a 'u,' but forty does not. In our experience, this is the most common number spelling mistake across all age groups, and it simply does not follow the pattern our brains expect.

• Ninty is wrong. The correct spelling is ninety. The word nine is there in full: ninety. Dropping the 'e' is easy to do when writing quickly, but it is consistently marked as an error.

• Eighthy is wrong. The correct spelling is eighty. Just like forty, eighty drops a letter you might expect to see. Students who have not been told this tend to add it back in.

• Eigth is wrong. The correct spelling is eighth. The 'h' from eight carries over into eighth, but the letters get rearranged in a way that feels awkward. Children tend to drop one without noticing.

• Fifty and fifteen are not the same. Easy to mix up in both spelling and speech. Fifteen ends in '-teen,' fifty ends in '-ty.' If you mean the number between fourteen and sixteen, it is fifteen.

• Hyphens in the wrong place. Twenty-one needs a hyphen. One hundred and twenty-one does not get a hyphen between one hundred and twenty-one. The hyphen only connects the tens and the ones.

A good habit to build is to slow down on any number word that contains a letter that doesn't appear in the digit's name. Those are almost always the ones that trip our children up.

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From "forty" to "ninety-nine," the way we write numbers in words follows rules we need to learn early.

Try It Yourself: Spell These Numbers

Time to put what we've covered to the test. Have your child try spelling out each of the numbers below.

• 14

• 40

• 18

• 92

• 47

• 80

• 68

• 12

• 99

• 100

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Through personalized learning plans and interactive teaching, Mathnasium helps students build both skills and confidence.

How Mathnasium Helps Students Build Solid Math Foundations

Mathnasium is a math-only learning center dedicated to helping K–12 students of all skill levels catch up, keep up, and get ahead in math.

Whether your young learner needs help building foundational skills like number sense or is ready to push further, we offer a personalized path forward, powered by our proprietary teaching approach, the Mathnasium Method™.

Our approach begins with a diagnostic assessment, a relaxed interaction that helps us pinpoint their strengths, knowledge gaps, and how they think about math overall.

With these insights, we create a personalized learning plan tailored to their needs and learning style.

Our specially trained tutors follow the plan, delivering face-to-face math instruction in a supportive and fun environment.

We use natural, everyday language to phrase math concepts as well as a mix of verbal, visual, mental, tactile, and written techniques to help students truly make sense of what they are learning.

When they get stuck, we break concepts down into manageable parts and explain both the how and the why. Over time, students develop the problem-solving skills and critical thinking tools they will carry with them in math and beyond.

Fun is a core part of every session. Our activities are hands-on and game-based, with plenty of rewards and consistent celebration of progress because confidence grows when students enjoy the process and see how far they have come.

And the results speak for themselves:

• 94% of parents report an improvement in their child's math skills and understanding

• 93% of parents report their child's improved attitude toward math after attending Mathnasium

• 90% of students saw an improvement in their school grades

For families in and around Frisco, TX, Mathnasium of Frisco East is a trusted local center recognized with multiple Reader's Choice Awards from Living Magazine for Best Tutoring, Best Early Education, and Best Summer Camp.

Whether your child is looking to catch up, keep up, or get ahead, our team is ready to help.

📅 Schedule a Free Diagnostic Assessment at Mathnasium of Frisco East

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Pssst! Check Your Answers Here

If you’ve given our exercise a try, check your spelling below:

• 14 — fourteen

• 40 — forty (not fourty)

• 18 — eighteen

• 92 — ninety-two (hyphen required)

• 47 — forty-seven (hyphen required)

• 80 — eighty (not eighthy)

• 68 — sixty-eight (hyphen required)

• 12 — twelve

• 99 — ninety-nine (hyphen required)

• 100 — one hundred

How did it go?