OpenAI Flex Pricing Calculator, Standard vs Flex vs Priority

OpenAI's synchronous API lets you pick a processing lane with the service_tier request field. The lane you choose changes latency, reliability, and, the part this tool computes, the per-token price. There are three lanes with distinct prices: Standard (default), Flex (flex), and Priority (priority). A fourth value, auto, lets OpenAI decide and has no distinct price, so it is out of scope here.

Every tier uses the same token-cost formula, with input and output priced separately because generating a token costs the model more compute than reading one:

1. Convert tokens to millions: inM = inputTokens ÷ 1,000,000 and outM = outputTokens ÷ 1,000,000.
2. Standard = (inM × stdIn + outM × stdOut) × requests, using the model's published Standard input and output prices per 1M tokens.
3. Flex = Standard × 0.5. Flex tokens are billed at OpenAI's Batch-API rate, which is exactly 50% of the Standard price for every supported model, so Flex is derived from Standard, never stored separately, and the 50% invariant can never drift.
4. Priority = (inM × prioIn + outM × prioOut) × requests, using the model's published Priority prices. Priority is nota flat multiple of Standard. It ranges from roughly 2× to 2.5× depending on the model, so each model carries its own Priority price. Where OpenAI has not published one (some nano and pro tiers), Priority is shown as "not published" rather than guessed.
5. Savings for a tier = Standard − tier, and the percentage divides that by the Standard total (guarded so a zero bill shows 0%, never a divide-by-zero).

The tool cross-checks Flex two independent ways, halving the Standard total, and applying the discounted per-million Flex rates directly to the tokens, and confirms they agree to the cent, the same "verified two ways" approach the tax calculator uses against the IRD's formula. Flex's trade-off is real: it runs slower, on a best-effort basis, and can return a 429 when capacity is unavailable, in which case you are not billed. Everything is computed in your browser from stored, dated prices. There are no network calls and no data leaves the page.

• OpenAI: Flex processing guide (Batch-rate pricing, 429 on unavailable)
• OpenAI: Priority processing guide (per-token premium for low latency)
• OpenAI: API pricing (Standard / Flex / Priority per-token rates)
• OpenAI: service_tier request parameter reference
• Central Bank of Sri Lanka: indicative USD→LKR rate

Standard and Priority per-token prices were last cross-checked against OpenAI's pricing page on 2026-07-13. Pricing is reviewed quarterly and after any OpenAI tier change. The Flex = 50% of Standard rule is a published, vendor-guaranteed term.