Is Grammarly Accurate? (a Proofreader Tells All)

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Grammarly is one of the most popular writing tools available, but how accurate is it? As a trained proofreader with experience using the free version (Grammarly Free) and currently using the paid version (Grammarly Pro), I can help you assess its precision—especially since I’ve put this software to the test!

Grammarly is sufficiently accurate for many people, given that it’s one of the leading proofreading and writing tools on the market. However, its accuracy wavers depending on a document’s complexity.

Let’s see how accurate Grammarly is and if it makes sense for you.

How Accurate Is Grammarly?

Quantifying Grammarly’s accuracy in a meaningful way is a tall order since several factors affect its precision.

Why It’s Difficult to Assess Grammarly’s Accuracy

It’s challenging to evaluate Grammarly’s accuracy because it performs better when used for a children’s book than a chemical engineering thesis.

An algorithm learns simple language before becoming more sophisticated and seeking to understand more complex language.

Grammarly may also be geared toward some style guides more than others.

Plus, because it receives feedback that helps improve its algorithm, it may perform better in some subject areas than others.

However, I assume you want to know if Grammarly is accurate enough for your intended use.

Soon, we’ll see how to evaluate Grammarly for your specific needs.

Putting Grammarly to the Test

In May of 2026, I evaluated Grammarly Free, Grammarly Pro, and Microsoft Editor using a nearly one-page document containing 24 total errors.

The errors inserted into the test document covered a variety of areas, including grammar, punctuation, spelling, and capitalization.

The document had a Flesch-Kincaid grade level of 5.1, meaning you’d need at least a fifth-grade reading level to comprehend what was written.

Here are the number of mistakes (out of 24) detected by each software:

• Microsoft Editor: 6
• Grammarly Free: 18
• Grammarly Pro: 18

When I performed the same test back in May of 2023, Grammarly Free caught only 12 errors in total. Its ability to catch basic errors, especially punctuation errors, has significantly improved.

What impressed me the most about Grammarly Free was its ability to fix blunders with homophones. For example, in the test document, Grammarly Free made the following corrections, which Microsoft Editor missed:

• changed eminent to imminent
• changed precede to proceed

Let’s hear it for Grammarly Free! 😊

If you’d like to read about the details of the assessment, you can find them in my article comparing Grammarly Free and Grammarly Pro.

Is Grammarly sufficiently accurate for my needs? Yes.

Specifically, I use Grammarly Pro as a final check when proofreading or copyediting my own articles and client documents. It helps me catch mistakes I may have missed. After all, a perfect proofreader doesn’t exist—even though we strive for perfection!

Could I use Grammarly Pro alone to do proofreading for clients? Absolutely not.

It plays a supporting role in the proofreading process. I use it as a backup.

Is Grammarly Accurate Enough for You?

Since your needs are unique, the crucial question is whether Grammarly is sufficiently accurate for you.

Is Grammarly Free Enough?

To test this, I recommend using Grammarly Free on a few pieces of writing.

Then, ask yourself this question: Is it finding mistakes I miss when proofreading my writing?

If it can catch and correct “enough” errors you’ve missed, it’s probably worth keeping. Only you can decide how many errors are “enough.”

Should I Go with Grammarly Pro?

If you want to further improve your writing, you may be interested in Grammarly Pro. If you’d like details about the features and prices of Grammarly Free and Grammarly Pro, please see my comparison article.

Grammarly occasionally offers a seven-day free trial for Grammarly Pro.

But if you forget to cancel the free trial before it ends, you’ll be charged (possibly for an annual plan).

If you opt to take the free trial for a test drive, here are a couple of questions to ask yourself to see if the fee is worth it:

1. Is my writing improving “enough” from the suggestions it offers?
2. Am I becoming a better writer due to learning from the recommendations?

If you answered yes to those questions, Grammarly Pro may be worth the investment.

If you answered no to those questions, my guess is that Grammarly Pro would be a waste of your time.

How Accurate Is Grammarly’s Plagiarism Checker?

Grammarly Pro comes with a plagiarism checker to ensure your writing is original. It compares what you’ve written to over 16 billion web pages as well as academic papers stored in ProQuest’s databases.

To assess this feature, I copied and pasted a portion of a Forbes article and a PubMed Central abstract into Microsoft Word and ran the plagiarism checker.

While Grammarly flagged 100% of the content from PubMed Central as plagiarized, it didn’t detect any plagiarism in the writing from Forbes.

It’s essential to note that although Grammarly checks your writing against billions of web pages, it doesn’t include all web pages.

Grammarly compares documents against the sources and databases it has access to. That’s why Grammarly’s explanation says, “Your document doesn’t match anything in our references.” So just because Grammarly failed to detect plagiarism doesn’t mean the content hasn’t been copied from somewhere else.

Based on my testing, Grammarly appears to have stronger coverage of scholarly articles and other frequently cited content.

Can Grammarly Be Wrong?

Yes, Grammarly can be wrong. Although Grammarly catches lots of slipups, its algorithm doesn’t fully grasp all the nuances of English.

Let’s look at some instances where Grammarly Free missed the mark, and then we’ll do the same for Grammarly Pro. Keep in mind that the writing in the screenshots is fairly simple. As writing gets more complex, Grammarly becomes more likely to miss mistakes.

I inserted several errors into one of my previous blog posts to give you an idea of where Grammarly can miss the mark.

Grammarly Free succeeded in catching the following flubs:

• the word have should be has
• a comma belongs after the word pointless
• vane should be vain
• a period should come after the word enjoyable

Grammarly Free failed to detect these blunders:

• there should be a closing quotation mark after (15 Basic Items).
• the word your should be you’re (but it gave us a hint by underlining this error in yellow)*
• the word begone should be beyond

*Grammarly Free underlines some potential errors or opportunities for improvement in yellow. To see the recommended fixes for these issues, you need to upgrade to Grammarly Pro.

Now let’s see how Grammarly Pro performed with the same test.

Grammarly Pro performed roughly the same as Grammarly Free when it came to finding mistakes.

However, it specifically recommended changing your to you’re. It also suggested changing the phrase can be done based (in the second sentence from the top) to depends to make the sentence more concise.

Grammarly Free used to offer suggestions to eliminate wordiness; however, it no longer does that. Instead, it has gotten better at finding grammar, spelling, and (especially) punctuation errors.

Catching missing quotation marks and parentheses is not Grammarly’s strong suit.

If you decide to use Grammarly, that’s one place it will need your help. And if you need software that checks for closing quotation marks, parentheses, and other consistency issues, PerfectIt may be a good solution for you.

It can also struggle with lapses in logic, like the above example, where it didn’t change the word begone to beyond. “Best wishes to you in your college days and begone” doesn’t sound quite right. 😉

Therefore, if you need a document to be as error-free as possible, your best bet is to hire a trained proofreader. They’ll be able to detect most of the mistakes that slip through the cracks of Grammarly’s algorithm.

How Does Grammarly Improve Its Accuracy?

Grammarly has made significant strides in improving its accuracy. A $90 million funding round led by General Catalyst enabled Grammarly to devote significant resources to fine-tuning its algorithm (source).

Improvements to Grammarly’s algorithm include increasing its accuracy in identifying errors and providing users with more accurate suggestions. Grammarly employs experts in natural language processing, machine learning, and linguistics to make these improvements (source).

Grammarly also relies on us to become more refined:

“AI systems also need feedback from humans. When lots of users hit “ignore” on a particular suggestion, for example, Grammarly’s computational linguists and researchers make adjustments to the algorithms behind that suggestion to make it more accurate and helpful.”

– Grammarly

Now we’ll see how we can make Grammarly work smarter (not harder) for our specific goals. 😊

Tips for Optimizing Grammarly’s Precision (Free vs. Pro)

Here are a few ways to improve Grammarly’s accuracy, depending on your needs.

1) Type in your primary language to get targeted suggestions.

Instead of having to select your primary language from a menu, Grammarly can now recognize the language you’re writing in as long as it’s one of the more than 20 languages Grammarly supports.

I tested this feature by randomly typing in Spanish in my otherwise English document, and Grammarly immediately started correcting my Spanish.

To learn more about the languages Grammarly supports and the types of suggestions available for each language, please see this page.

2) Select your preferred English dialect.

Grammarly recognizes five styles of English: American, British, Canadian, Australian, and Indian.

Selecting the appropriate style is necessary since English dialects differ in spelling, punctuation, and grammar.

3) Add words to your personal dictionary.

If you use words that Grammarly doesn’t recognize, you can add them to your personal dictionary so they won’t be flagged unnecessarily.

For example, I had a client who sometimes used the scientific names of bacteria.

If I didn’t want Grammarly to flag those terms every time they came up, I could have added them to my dictionary once I was sure of the correct spelling.

4) Turn off writing preferences as needed. (Grammarly Pro only)

Grammarly Pro allows you to turn off writing preferences you don’t want.

Below are the first several preferences from a long list that can be toggled on or off. Each one comes with an explanation so you know precisely what Grammarly will recommend.

I keep all of the preferences toggled on. In the past, the only suggestion I deactivated was one that flagged sentence-ending prepositions. In a blog article, ending a sentence with a preposition is perfectly acceptable, so that was a recommendation I didn’t need to deal with. 😉

However, Grammarly has since removed that preference because ending sentences with prepositions is now acceptable, even in formal writing.

One Final Tip: Help Grammarly to Help You

As we know, Grammarly isn’t 100% accurate, so be sure to research any suggestions that seem iffy.

By doing this, you’ll learn more about grammar and punctuation and be better prepared to keep or discard Grammarly’s recommendations.

I hope this article has helped you understand Grammarly’s level of accuracy, why it’s not always right, and how it’s improving.

If you’d like to know more about Grammarly’s functionality, please check out this article about what Grammarly can and can’t do.

Best wishes to you!

“When things do not go your way, remember that every challenge—every adversity—contains within it the seeds of opportunity and growth.”

– Roy T. Bennett