What it means
WhatsApp does not charge per message. It charges per conversation window. When a customer sends the first message to your business, a 24-hour window opens. During that window your business can reply with anything (free-form text, images, documents, even utility templates) at no extra cost from Meta. Each new customer message resets the 24-hour clock.
Click-to-WhatsApp ads get a longer 72-hour free window from Meta, since the ad click is treated as the implicit start of the conversation.
Outside an active window, if your business needs to initiate (a broadcast, a reminder, a re-engagement), you pay a template fee. Meta charges three rates: Marketing, Utility, and Authentication.
Why it matters
Most cost surprises on WhatsApp come from misunderstanding the window. Teams who reply to customers within 24 hours pay almost nothing. Teams who let messages pile up and have to send a template message the next day suddenly see a bill.
Designing your AI agent and team workflow to respond inside the free window is the single biggest lever for keeping WhatsApp costs predictable. The cost calculator on this site assumes a healthy mix of customer-initiated (free) and business-initiated (paid) volume.
Example
A spa owner sees 200 enquiries a month. Of those, 180 are replied to within 24 hours by an AI agent (free). The remaining 20 require a follow-up reminder the next day, which uses a utility template (small per-message fee). Total Meta bill: SGD 8 a month, not SGD 80.