# Exponential backoff

> Exponential backoff is the retry strategy of waiting longer after each failed attempt (1 s, 2 s, 4 s, 8 s…), used for 429 and 5xx responses so that retries do not amplify an overload.

When a request fails for a transient reason, retrying immediately and repeatedly makes things worse for everyone. Backoff spaces retries out, usually with some random jitter, and gives up after a fixed number of attempts. For 429 responses the server's `Retry-After` header takes precedence over the schedule.

Backoff only makes sense with idempotency: a retried send must not become a duplicate.

At SMSMeteor: the recommended policy is to retry 429 after `Retry-After` and 5xx with backoff from one second over five attempts, reusing the same idempotency key, and never to retry other 4xx.

Related terms: [Idempotency key](https://smsmeteor.com/glossary/idempotency-key), [Rate limit](https://smsmeteor.com/glossary/rate-limit), [Webhook](https://smsmeteor.com/glossary/webhook)

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