Grammarly works on text you are already writing, inside your email and documents. ChatGPT writes a draft from your instructions. They help at different stages of the same job, and many people use both.
Prices and features below are as of October 2026. Check the official pages before you pay.
The short verdict
Pick Grammarly if:
- You write most things yourself and want them clear and free of mistakes.
- You write in many apps, such as Gmail, Word, Google Docs and Slack, and want help in each of them.
- English is not your first language and you want suggestions as you type.
Pick ChatGPT if:
- You want a first draft from a short brief, such as a reply, a post or a proposal.
- You also want help with planning, research and summaries.
Use both if you draft with AI and still want a final check before you hit send.
What Grammarly does
Grammarly checks your text where you write it. It runs as a browser extension in Chrome, Safari, Firefox and Edge, and as a desktop app for Windows and Mac. It works in Gmail, Outlook, Word, Google Docs and Slack, among others (where Grammarly works).
From the Grammarly plans page:
- Free: catches mistakes, shows how your tone comes across, and includes 100 AI prompts a month.
- Pro: adds tone changes, full-sentence rewrites, plagiarism and AI-text detection, and 2,000 AI prompts per member a month. For teams it adds one shared style guide and one brand tone.
- Enterprise: unlimited prompts, style guides and brand tones, plus security and admin controls.
The strength is that it stays out of the way. You keep writing, and it underlines what to fix.
What ChatGPT does
ChatGPT writes from instructions. You give it the task, the facts and your rules, and it drafts the whole piece. It can also explain a topic, summarise a long document, or turn notes into a plan.
To make its drafts sound like you, save your rules in custom instructions, which apply to every chat (custom instructions). The full method is in how to make AI sound like you.
The trade-off is that you work in a separate window and copy the result out.
The same email, two ways
You need to tell a customer their order is late.
With Grammarly: you write the email yourself in Gmail. Grammarly fixes a typo, flags a long sentence and suggests a calmer tone for one line. The email is still yours, word for word.
With ChatGPT: you write a brief with the order details and your voice rules. It returns a full draft. You edit it, check the dates, and paste it into Gmail.
We are reaching out to inform you that unfortunately there has been an unexpected delay with regards to your order.
Your order is running three days late. It will ship on Friday. Sorry for the wait.
Either tool can help you get from the first line to the second. ChatGPT gets there if your brief asks for short and plain. Grammarly gets there if you accept its suggestions.
Price
- Grammarly Pro: $12 per member a month billed yearly ($144 a year), or $30 billed monthly (Grammarly Pro pricing).
- ChatGPT: Free, Go at $8 a month in the US, Plus at $20 a month and Pro from $100 a month (ChatGPT pricing).
Both have free plans. Start there and see which one you open more.
Brand rules in each tool
If you write for a brand, both can hold some rules. Grammarly Pro stores a style guide and a brand tone for a team. ChatGPT holds rules in custom instructions or a project.
Neither replaces a written voice guide that a person checks. The brand voice guidelines template gives you one page to keep in both.
How to decide
- If you mostly start from a blank page, try ChatGPT first.
- If you mostly write your own words and want them cleaner, try Grammarly first.
- Use each on free plans for a week, on real emails and posts.
- Count the time saved per message, and note which one you missed when it was off.
If you want to compare ChatGPT with another drafting tool, see ChatGPT vs Claude for writing.