The most common proofreading mistakes (and why they matter)

Proofreading isn’t just about spotting a typo here and there. It’s about quality control. It’s the final step that prevents you from publishing something that looks careless or confuses the reader. And, having proofread thousands of words in marketing content, blogs, brochures, and websites, I see the same proofreading mistakes crop up time and time again.

What proofreading mistakes should you look for?

So, to help you ensure your content is polished and error-free, here are some of the most common errors I come across and why they’re worth paying attention to.

1. Homophones - they sound right, but are wrong

Homophones are words that sound the same but are spelt differently. But, crucially, they have different meanings.

They can slip through spellcheck because they’re technically real words, just not the right ones. Homophones can sneak through unnoticed, especially when you’re writing technical specs or writing on a deadline.

Examples of homophones:

• Affect, effect

• Compliment, complement

• Its, it’s

• Principle, principal

• Their, there, they’re

• Your, you’re

  
  

In context:

❌ You’re external wall cladding system has been approved

✅ Your external wall cladding system has been approved.

❌ This colour palette really compliments the client’s brand

✅ This colour palette really complements the client’s brand.

When used incorrectly, homophones look unprofessional, especially in tender submissions, case studies, or product brochures.

2. Inconsistencies - an unprofessional mish-mash

Inconsistencies can be subtle, but you can’t unsee them once you spot them. They creep in during writing, editing, design or layout stages. Individually, they might look fine. But side-by-side on a website, brochure or LinkedIn post, they scream at you and make your brand look sloppy.

When proofing something, look for written inconsistencies such as formatting, spelling, and punctuation and layout/design discrepancies, including font sizes, alignment, and heading styles.

Common inconsistencies:

• Times: 10 am, 10:00 AM or ten o’clock

• Dates: 1 January 2025, 1st January 2025, 01.01.2025

• Quote marks: “double” or ‘single’

• Headings: Some in UPPER CASE, others in Sentence case

• Compound words: co-ordinate or coordinate, sub-contractor, subcontractor or subcontractor

• Spelling: UK or US (organise vs organise, specialise vs specialize, favourite vs favorite)

• Spacing: inconsistent use of single/double space after full stops.

  
  

Example:

❌ Our site hours are 7.00 AM – 5pm. 7am to 5pm on weekdays.

✅ Our site hours are 7am – 5pm, Monday to Friday.

I've seen loads of inconsistencies when proofreading and editing copy. Many of these crop up when different people have written the content. But consistency is essential, especially for a B2B company where audiences and customers expect professionalism.

3. Incorrect word choice - changes meaning

Using the wrong word, even if it looks ‘close enough,’ can change the meaning of a sentence or make it confusing. Sometimes, it’s the wrong preposition, verb form or something that looks right but isn’t.

Examples to watch for:

• Accept and except

• Advise and advice

• Affect and effect

• Fewer and less

• Insure and ensure

• Than and then

In context:

❌ There are less people at the event this year.

✅ There are fewer people at the event this year.

❌ She gave me some great marketing advise.

✅ She gave me some great marketing advice.

❌ The new surface treatment will effect the lifespan of the panels.

✅ The new surface treatment will affect the lifespan of the panels.

Less is used when something can’t be measured or counted, and fewer is when you can put a number to things and count them.

Advise is a verb that you use to give guidance, encouragement or a suggestion. Advice is a noun that refers to guidance, encouragement, or suggestion.

Effect is a noun and the result or consequence of something, while affect is the verb to alter, influence or impact something.

This is where proofreading makes the difference between ‘good enough’ and polished, professional.

4. The dreaded apostrophe - small but a big problem

Few punctuation marks cause more confusion. The apostrophe is often misused. It’s either missing when it should be there or included when it shouldn’t.

I was always taught that you should use an apostrophe:

• To show possession: the contractor’s report

• When a letter is missing, it is often called a contraction: can’t, you’re, or it’s.

Common mistakes:

❌ Its a durable, low-maintenance surface.

✅ It’s  a durable, low-maintenance surface.

❌ We’ve completed over 30 installations on the client’s roofs.

✅ We’ve completed over 30 installations on the clients’ roof’s.

❌ All project's must be signed off before handover.

✅ All projects must be signed off before handover.

When in doubt, read it out loud. If “it is” fits, use” it’s.” If not, leave it as “its.” Misuse of the apostrophe points to carelessness. It’s not a good look when trying to win new business or build trust amongst your audience.

5. Commas - don't forget them, but use them wisely

Commas break a sentence up, help the reader breathe, and clarify meaning. Used well, they guide a person smoothly through a sentence. Poorly used (or not at all), they can cause confusion or even change the meaning completely.

Common issues:

Missing after introductory phrases

❌ After the walls were painted the team installed the lighting.

✅ After the walls were painted, the team installed the lighting.

Unclear separation in lists

❌ We supply doors windows flooring and lighting.

✅ We supply doors, windows, flooring, and lighting.

Misplaced commas splitting the subject and the verb

❌ Our installation team, is fully accredited.

✅ Our installation team is fully accredited.

Misunderstood clauses

❌ We installed the new signage, because the old one was damaged.

✅ We installed the new signage because the old one was damaged.

Getting commas right improves clarity and flow, especially in longer technical or descriptive content.

6. Questions and question marks - ask correctly

Surprisingly, forgetting to use a question mark when a sentence is a question and overusing it when it’s not are common mistakes. If you’re asking someone something directly, it needs a question mark. If you’re making a statement, it doesn’t.

Examples:

❌ Would you like us to provide samples for the meeting.

✅ Would you like us to provide samples for the meeting?

❌ Let us know if you’d like a site visit?

✅ Let us know if you’d like a site visit (this is a statement, not a question).

7. And and finally, repeated words

Repeated words are one of the easiest mistakes to miss, especially when editing your work or writing something quickly. Your brain skips over the repeated word because it’s already read it in the first instance.

This often happens when cutting and rearranging sentences during editing or copying text between documents.

In context:

❌ The contractor confirmed that that the project is on schedule.

❌ Our team is ready to to assist with any technical queries.

A repeated word might seem harmless, but it interrupts the flow and distracts the reader. Repetitions can be subtle, but when you’re positioning yourself as a professional, you want to clean up these typos.

Proofread your content - it's worth taking your time

These proofreading mistakes might seem petty. But when they affect how people see your business, they matter. It's worth getting the details right. Proofreading helps you to produce consistent, credible and confidently written content.

Need a fresh pair of eyes on your content? I’d be happy to take a look.

I'm a professional copywriter, copy editor and proofreader. If you need help creating content, editing or proofreading, get in touch, and let's talk; I'm here to help.