Grammarly costs $12 per month for Pro, QuillBot's Premium plan runs $4.17 per month when billed annually, and ProWritingAid offers several tiers ranging from a $30 monthly Premium plan to a $699 lifetime Premium Pro license.
Those three numbers cover the main paid options among the writing assistants in our database, and the gap between them is wider than most people expect. According to our AI tool database, Grammarly's Free tier covers basic writing help, Pro is listed at $12/mo, and Enterprise pricing is custom. The same database records QuillBot's Free plan at $0, Premium at $4.17/mo on the annual plan, and Team pricing as custom. ProWritingAid's snapshot shows Free, Premium at $30/mo or $360/yr, Premium Pro at $12/mo or $144/yr, and lifetime licenses at $399 and $699.
The reason these prices diverge so much comes down to what each company is actually selling you. Grammarly's paid tier is built around context-aware style adjustment — the tool reads whether you're writing an academic paper, a business memo, or an email, and shifts its suggestions to match.
It also does logic and structure work through features like Smart Drafts, which means it's editing at the paragraph level, not just the sentence level. QuillBot's strength is rewriting and paraphrasing, so its Premium tier is priced low to pull people into a habit of running text through it repeatedly.
ProWritingAid sits closer to a full editing suite, with deep reports on style, pacing, and repetition — the kind of analysis a fiction writer or long-form editor wants. Different jobs, different price points.
Here's a concrete example. Say you write about 20,000 words a month — roughly ten blog posts or a short report. On Grammarly Pro at $12/mo, that's a flat cost regardless of volume.
On QuillBot Premium at $4.17/mo billed annually, you pay less, but you're mostly getting paraphrase and grammar help rather than structural feedback. If you wanted ProWritingAid's Premium Pro tier at $12/mo, you'd get the deeper style reports, and if you planned to keep using it for years, the $699 lifetime Premium Pro license would eventually beat the subscription — though only after a long stretch, and only if you're confident you'll still want the tool.
The lifetime option is the one genuinely unusual thing in this comparison, because most AI writing tools don't offer one at all.
The honest limits matter here. First, pricing on AI tools changes often — the figures above come from a snapshot recorded on 2026-09-18, so check each vendor's own page before you buy, especially for annual plans and lifetime deals. Second, the cheapest plan isn't automatically the best value: QuillBot's $4.17/mo annual price requires paying upfront for a year, and if you stop using it after two months you've spent more than three months of Grammarly Pro would have cost.
Third, none of these tools replace a human editor for anything you're publishing under your own name — they catch patterns, not arguments. Fourth, if you only write occasionally, the free tiers from all three may be enough, and paying for a subscription you open twice a month is the most common waste we see.
Start free, track how often you actually hit the paywall, and only then pick a tier. If you're weighing whether any AI writing tool is worth paying for at all, it helps to know where free options genuinely stop being free.