The OpenAI API doesn’t charge a flat monthly fee. You pay for tokens: the text you send (input) and the text the model writes back (output), each priced per million tokens. That makes bills hard to predict until you put in real numbers. This OpenAI API cost calculator does the maths per request, per day and per month, in dollars, naira or six other currencies.
How it works
- Cost per request = input tokens × input price + output tokens × output price, with prices in US dollars per million tokens from each vendor's official API pricing page (checked 9 Oct 2026).
- Cost per day = cost per request × requests per day. Cost per month = cost per day × the days per month you enter (30 by default).
- We use each model's standard short-context rate. Long prompts, batch processing, prompt caching, fast modes, tools such as web search, and taxes are priced differently and are not included.
- Totals are converted at daily exchange rates from ExchangeRate-API. Your card or bank may add its own markup.
Frequently asked questions
How is OpenAI API cost calculated?
OpenAI charges per million tokens, with separate prices for input (your prompt) and output (the reply). For example GPT-6.1 Sol is $2 per million input tokens and $10 per million output tokens on the standard tier for prompts up to 272K tokens. Multiply your tokens by those rates and by your number of requests.
What is the cheapest OpenAI model?
Of the current models in our list, GPT-6 Luna is the cheapest at $0.1 per million input tokens and $0.5 per million output tokens. Cheaper models are usually less capable, so test quality before switching.
Is the OpenAI API cheaper than ChatGPT Plus?
It depends on how much you use. Light, simple use can cost less than a $20 subscription, but heavy use of a top model can cost far more. Enter your real usage here and compare with the subscription price on our ChatGPT Plus price page.
Does this include batch, caching or long-context prices?
No. We use the standard short-context rate. OpenAI's pricing page lists lower batch and flex rates, cheaper cached input, and higher rates for long prompts and fast modes.
How many tokens is a word?
For English, a rough rule is about 4 characters or three-quarters of a word per token. Paste your prompt into our token counter for a quick estimate.
As an example from OpenAI’s pricing page on 9 October 2026: GPT-6.1 Sol costs $2 per million input tokens and $10 per million output tokens on the standard tier. A chatbot that sends 1,000 input tokens and gets 500 output tokens back, 100 times a day, costs about $0.007 a request, $0.70 a day and around $21 a month. The same usage on GPT-6 Luna ($0.10 / $0.50) is about $1.05 a month.
Compare with Claude, Gemini and Grok
Open Compare the same usage under the result to rank more than 30 models from OpenAI, Anthropic, Google and xAI by monthly cost for exactly your workload. Prices for each come from the vendor’s own pricing page, and the result links to it.
What the estimate doesn’t include
- Long prompts: OpenAI charges more once input goes over 272K tokens, and other vendors have their own thresholds. The calculator warns you when you pass one.
- Discounts: batch processing, flex processing and cached input are cheaper than the standard rate we use.
- Extras: fast modes, web search, file search, images and audio are priced separately.
- Bank and tax: add your card’s FX markup and any VAT in the optional box.
Not sure how many tokens your prompt uses? Paste it into the token counter first. And if you only chat with ChatGPT rather than build with the API, the ChatGPT Plus price page is what you need, since the subscription and the API are billed separately.