How many SMS per month is too many?

There is no number, but there is a signal that tells you when you have gone past it.

The signal

Your opt-out rate per campaign. If it stays stable, you are fine. If it rises with every send, you are going too fast — regardless of how much you send.

Why SMS is stricter than email

An SMS interrupts. An email waits in an inbox. What feels normal in email quickly feels intrusive in SMS — expect a fraction of the frequency you would use for mail.

Transactional does not count

An order confirmation, an appointment reminder or a shipping notice is not experienced as frequency. You can send those as often as there are events.

Say it up front

Anyone told at sign-up how often you send experiences that same number as less. The irritation comes from an expectation that does not match.

Differentiate

People who click tolerate more. People who have done nothing for six months should get less — or you ask once whether they want to stay.