Most AI writing tools sell a monthly plan. Very few tell you what one finished article costs, and that is the number that decides whether a content programme pays for itself.
This guide shows how to work it out for the two billing models you will meet in WordPress AI writing:
- Word-credit plans. You buy an allowance of words, and every article draws it down. We use Koala.sh as the worked example because its pricing page is unusually explicit about how the count works.
- Bring-your-own-key (BYOK) plugins. You pay a licence, connect your own AI provider account, and the provider bills you per token. WP Content Writer Pro, which we make, works this way.
All prices were checked on 13 October 2026. Prices change, so the method matters more than the figures. Once you have the method you can re-run it whenever a vendor changes its price list.
The formula for word-credit plans
The naive calculation divides the plan price by its word allowance and multiplies by article length. It leaves out two variables that can double or triple the result.
Cost per article = plan price ÷ (allowance ÷ model multiplier ÷ words per article) ÷ utilisation
Taking each term in turn:
- Allowance is the headline word count. Koala Starter is $25 for 45,000 words a month.
- Model multiplier is how many allowance words one generated word costs. Koala’s footnote reads: “The word count is based on using GPT-6 Luna. GPT-6 Sol and Claude Sonnet 5 count words at 2x, and Claude Opus 5.5 counts at 3x.”
- Words per article is your typical finished length. We use 1,500 below.
- Utilisation is the share of the allowance you actually use before it expires. Koala’s monthly credits expire after a month. Annual credits arrive up front and last a year, which is more forgiving.
Worked example: Koala Starter
45,000 words ÷ 1,500 = 30 articles on GPT-6 Luna. $25 ÷ 30 = $0.83 per article, if you use the full allowance.
Switch to Claude Sonnet 5 and the 2x multiplier gives 45,000 ÷ 2 ÷ 1,500 = 15 articles, so $1.67 per article.
Now suppose you only publish 10 Sonnet articles that month, using 10 of the 15 the plan allows. Utilisation is 67%, and the real cost is $25 ÷ 10 = $2.50 per article. The headline price has not changed, but your cost per article has tripled.
The full Koala ladder, per article
At 1,500 words and full utilisation, monthly billing:
| Plan | Price | Per article, Luna (1x) | Per article, Sonnet 5 (2x) | Per article, Opus 5.5 (3x) |
|---|---|---|---|---|
| Starter | $25 | $0.83 | $1.67 | $2.50 |
| Professional | $49 | $0.74 | $1.47 | $2.21 |
| Boost | $99 | $0.59 | $1.19 | $1.78 |
| Growth | $179 | $0.54 | $1.07 | $1.61 |
| Elite | $350 | $0.53 | $1.05 | $1.58 |
| Scale III | $2,000 | $0.30 | $0.60 | $0.90 |
Annual billing takes 20% off every figure. Bigger plans are cheaper per word, as you would expect, but the multiplier has a much larger effect than the plan tier. Opus on Scale III costs more per article than Luna on Starter.
One caveat: Koala’s plans also include “credits”, a separate currency for its keyword, competitor, backlink and SERP research tools. They are not counted in the per-article figures above, but they are real value if you would otherwise pay for a separate SEO tool.
The formula for bring-your-own-key
BYOK splits the cost into two parts. One is fixed and one varies with use:
Cost per article = (licence ÷ articles per month) + provider cost per article
Step 1: turn words into tokens
AI providers bill per million tokens, not per word. For English prose, one word comes to about 1.33 tokens, so a 1,500-word article is roughly 2,000 output tokens.
Step 2: account for input
One article is never one API call. A sound pipeline runs research, an outline, the body, metadata and often a humanising pass, and each step re-sends context that is billed as input. Our cost calculator counts input at 1.5x output. If your prompts are long or your research step pulls in a lot of source material, raise that ratio.
Step 3: apply the provider’s rates
Using the per-million-token rates in the WP Content Writer Pro plugin’s pricing table:
| Model | Input / output per 1M tokens | Est. cost, 1,500-word article |
|---|---|---|
| Claude Sonnet 5 | $3 / $15 | ~$0.039 |
| Claude Haiku 4.5 | $1 / $5 | ~$0.013 |
| Gemini 2.5 Flash | $0.30 / $2.50 | ~$0.006 |
| GPT-5 mini | $0.25 / $2 | ~$0.005 |
Here is the Sonnet 5 sum written out: 1,500 × 1.33 ≈ 1,995 output tokens × $15/M = $0.030. Input is 1,995 × 1.5 ≈ 2,993 tokens × $3/M = $0.009. The total is about $0.039.
Treat these as orders of magnitude, not quotes. Providers revise prices, and a few rates in the plugin’s table are marked as its own estimates. The figure that counts for your site is in the plugin’s usage log, which records real tokens and an estimated cost for each call, grouped by the article that caused it.
Step 4: spread the licence across your output
WP Content Writer Pro costs $9 a month for one site, $19.99 for five and $49.99 for fifteen, with no word cap from us. The licence is fixed, so its share per article falls as you publish more:
| Articles / month on one site | Licence share | + Sonnet 5 usage | Cost per article |
|---|---|---|---|
| 10 | $0.90 | $0.039 | ~$0.94 |
| 30 | $0.30 | $0.039 | ~$0.34 |
| 100 | $0.09 | $0.039 | ~$0.13 |
The utilisation problem works the other way here. On a word-credit plan, publishing less than you planned raises your cost per article because you paid for words you did not use. On BYOK, publishing less only means the fixed licence is spread over fewer articles, and the provider bill shrinks with it.
Putting the two side by side
Same site, same 1,500-word articles, writing on Claude Sonnet 5, monthly billing:
| Articles / month | Koala plan needed | Koala per article | BYOK (WPCWP Starter) per article |
|---|---|---|---|
| 10 | Starter, $25 | $2.50 | ~$0.94 |
| 30 | Professional, $49 | $1.63 | ~$0.34 |
| 100 | Growth, $179 | $1.79 | ~$0.13 |
The Koala column does not fall steadily. At 30 articles you need Professional, not Starter, because 30 Sonnet articles use 90,000 counted words. At 100 articles you have to step up to Growth. Each step up the ladder comes with spare allowance you are paying for but may not use.
We have a full head-to-head on plans, trials and refunds in WP Content Writer Pro vs Koala.sh pricing.
The costs neither price list shows
A per-article figure is only as honest as what it includes. Before you commit to either model, check these.
Refreshing old posts
Updating a 2,000-word article that has started losing rankings costs about as much as writing it again. On a word-credit plan it comes out of the same allowance as new content. On BYOK it costs only tokens. If your strategy leans on keeping a back catalogue current, add your refresh volume to the “words per month” figure before choosing a Koala tier.
Failed and discarded generations
Not every draft is usable. If one in five gets thrown away, every cost per article above rises by 25% under both models. Guardrails that hold a weak draft back for review, rather than publishing it, do not avoid the cost. They do stop it from also costing you rankings.
Fact-checking and images
A second model reviewing the first model’s facts is an extra call. On BYOK you pay for it in tokens. Choose a cheap model for the review pass and the cost stays small, but it is not zero, and the table above leaves it out. The same goes for AI-generated images. Stock photos from a licensed library cost nothing in tokens, while generated images are billed by your provider.
Batch discounts
This one works in your favour. Anthropic and OpenAI both offer batch APIs at roughly half the per-token price, for work that does not need an instant reply. WP Content Writer Pro sends bulk jobs that way, so for a scheduled bulk run the real provider cost can be well below the estimates above.
Your time
BYOK means one more account, one more invoice and a bill you need to keep an eye on. A word-credit plan wraps all of that into one fixed price. For a solo writer publishing a handful of posts a month, that simplicity can be worth more than the difference in cost per article. Be honest with yourself about this line.
What is bundled
Koala’s subscription includes SEO research credits, live Amazon data for affiliate content and publishing to Shopify, Webflow and Ghost. If you would otherwise pay for those separately, subtract that from Koala’s effective price before comparing. If you would not use them, they add nothing.
A spreadsheet you can build in ten minutes
Use one row per tool and these columns:
- Monthly price (or annual ÷ 12)
- Articles you will really publish, new plus refreshed
- Average words per article
- Model multiplier (word-credit plans), or provider cost per article (BYOK), from the vendor’s page or the calculator
- Plan needed: the cheapest tier whose allowance covers articles × words × multiplier
- Discard rate: start at 10–20% until you have your own data
- Cost per published article = (price of plan needed + provider cost × articles) ÷ (articles × (1 − discard rate))
Run it at your current volume and at double. The model that wins at both is your answer. If the winner changes between the two, pick the one that suits where you expect to be in six months, not where you are today.
The short version
Word-credit plans charge for volume and for model quality, and you lose whatever allowance you do not use. BYOK charges a fixed fee for access, and you pay the provider’s raw rate for usage. With credits, your cost per article can rise when you publish less or choose a better model. With BYOK it falls as you publish more and does not depend on the model beyond the provider’s own rate difference.
For more on how providers, keys and failover work in practice, see our AI providers documentation and AI content generation inside WordPress. When you are ready to test the numbers on your own site, the 7-day trial needs no card, and the usage log will show your real cost per article within the first day.
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