--- title: API rate limits description: Details about API rate limits and fair use. --- [Skip to content](https://support.postworks.co.uk/knowledge/api-rate-limits#main-content) ![Logo (transparent background, red emblem, red text, tagline NOT included) (PRIVATE).png\]](https://support.postworks.co.uk/hs-fs/hubfs/Logo%20(transparent%20background%2c%20red%20emblem%2c%20red%20text%2c%20tagline%20NOT%20included)%20(PRIVATE).png?height=40&name=Logo%20(transparent%20background%2c%20red%20emblem%2c%20red%20text%2c%20tagline%20NOT%20included)%20(PRIVATE).png) Open main navigation Close main navigation - [Postworks Portal](https://app.postworks.co.uk/dashboard/send) [Postworks Portal](https://app.postworks.co.uk/dashboard/send) Hello. How can we help you? - There are no suggestions because the search field is empty. 1. [Support Centre](https://support.postworks.co.uk/knowledge?hsLang=en) 2. [Postworks API](https://support.postworks.co.uk/knowledge/postworks-api?hsLang=en) 3. [API reference](https://support.postworks.co.uk/knowledge/postworks-api?hsLang=en#api-reference) # API rate limits ## Details about API rate limits and fair use. In order to maintain optimal performance of our API and ensure that all partners and customers have a great experience we urge all developers and partners to consider and optimise their calls and flows. ### General limits - Concurrent Limit: 5 calls in progress at one time - Minute Limit: 60 calls per minute - Daily Limit: 50,000 calls per day ### Send limits - Synchronous document submission - `/v2/send/document`: 60 calls per minute - Asynchronous document submission - `/v2/send/documentAsync`: 180 calls per minute ### Exceeding a rate limit Exceeding a rate limit will result in an `HTTP 429` (too many requests) response. It will include an `X-Rate-Limit-Problem` header telling you which limit you have reached. If you have exceed the minute or daily limit you will also receive a `Retry-After` http header that tells you how many seconds to wait before making another request. Requests are counted against a fixed window which will reset at different times for each tenant. It is important to use the Retry-After header to know when you can start making calls again. While not all endpoints and limits are currently being enforced, we urge our partners to optimise calls and flows according to these limits, in order to maintain optimal performance.   - [Send Letters](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#main-content) - [Preparing your documents](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#preparing-your-documents) - [Sending via Web Portal](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#sending-via-web-portal) - [PDFs containing multiple recipients (mailmerges)](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#pdfs-containing-multiple-recipients-mailmerges) - [User Management](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#user-management) - [Reports](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#reports) - [Account Top-up](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#account-top-up) - [Quick Start Guide](https://support.postworks.co.uk/knowledge/send-letters?hsLang=en#quick-start-guide) - 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