AI API Budget Calculator — how many tokens and requests your money buys

Every large-language-model API prices two things separately: the input tokens you send (your prompt, system message, and any context) and the outputtokens the model writes back. Prices are quoted in US dollars per 1,000,000 tokens, and output is almost always dearer than input because the model spends compute generating each token. This calculator reads those published per-million prices from the same shared table used by the site's AI API Cost Calculator, so the two tools never disagree.

Most cost calculators go usage → cost. This one runs the arithmetic backwards — budget → capacity — in six steps:

1. Cost per request. Creq = (Tin ÷ 1,000,000 × Pin) + (Tout ÷ 1,000,000 × Pout) where Tin/Tout are your average input/output tokens and Pin/Poutare the model's per-million prices.
2. Requests affordable. Nreq = floor(Budget ÷ Creq). We floor to whole requests — you can't buy a fraction of a call — with a tiny epsilon guard so exact-multiple budgets (say a budget that divides evenly into 100 requests) don't drop to 99 through floating-point rounding.
3. Total tokens. Ttot = Nreq × (Tin + Tout), split back into input and output shares.
4. Words. Using OpenAI's rule of thumb of about 1.33 tokens per English word, Words = round(Ttot ÷ 1.33).
5. Pages. At roughly 500 words per A4 page, Pages = round(Words ÷ 500).
6. Runway. If you enter requests per day R, Days = floor(Nreq ÷ R). Any dollar figure is multiplied by your USD→LKR rate for the rupee lines.

There is no opinion or estimation model here — just arithmetic over authoritative published prices. As an independent check, the tool re-derives the cost per request through a per-1,000-token unit instead of the per-1,000,000-token path and confirms both produce the same number of affordable requests, the same way the site's tax calculator cross-checks itself against the IRD's monthly formula. The words and pages figures are approximations for human-scale framing; the request, token, and dollar numbers are exact.

• OpenAI — API pricing (per-1M input/output token prices)
• Anthropic — Claude API pricing
• Google — Gemini API pricing
• OpenAI Help — What are tokens and how to count them (words ≈ tokens ÷ 1.33)
• Central Bank of Sri Lanka — daily indicative USD/LKR rate

Prices were last cross-checked against the vendor pricing pages on 2026-07-01. The shared price table is reviewed roughly quarterly and whenever a vendor moves a tier.