The WhatsApp 24-hour window: what you can send, when
After a customer writes to you, free-form replies are open for 24 hours. What opens the window, what closes it, and what changes once it shuts.
· 6 min read
One rule explains most of WhatsApp's business behaviour
Almost every confusing thing about business messaging on WhatsApp follows from a single rule: a business can send whatever it likes, in its own words, only inside a limited period after the customer has messaged first. That period is the customer service window, and it runs for 24 hours from the customer's most recent message. Inside it, a business replies freely. Outside it, the only thing that can be sent is a template that Meta has already approved.
This is not an arbitrary restriction. It is the mechanism that makes WhatsApp usable at all. The platform's value to the people using it rests on their inbox not filling with messages from businesses they never contacted, and the window is how that is enforced structurally rather than by policing intent after the fact. A business that understands the window stops experiencing WhatsApp as a set of unpredictable rules and starts seeing one consistent principle applied everywhere.
It also reframes what a business should optimise for. If free-form conversation is only available after a customer initiates, then getting the customer to initiate — and replying while they are still there — is worth considerably more than finding clever ways to push messages outward.
What opens the window, and what does not
The ordinary way the window opens is the obvious one: the customer sends the business a message. Any inbound message from that person resets the clock, so an active back-and-forth conversation keeps renewing itself for as long as the customer keeps replying. The window is per customer, not per business: having an open window with one person says nothing about anyone else.
There are also qualifying free entry points. A customer arriving through a Click-to-WhatsApp advertisement, for instance, opens a conversation in a way that Meta treats favourably, because the person has demonstrably chosen to start talking to the business. The important shared feature is that in every case the customer acted. Nothing the business does on its own — adding a number to a list, importing contacts, sending a template — opens a free-form window by itself.
What does not open a window is worth stating plainly, because assuming otherwise is a common and expensive mistake. Having someone's phone number does not. A past purchase does not. A form filled in on a website does not, though it may constitute consent to receive templates, which is a different thing. Consent to be messaged and an open window are two separate concepts, and confusing them leads a business to expect free-form replies to work when only a template will.
Inside the window: reply in your own words
Inside an open window, the business is not constrained by templates. It can answer a question, send a photograph of the item in stock, apologise for a delay, quote a price, or ask a clarifying question, all in ordinary language written at the time. These are session messages, and they behave the way anyone would intuitively expect a chat to behave.
This is where WhatsApp is genuinely at its best as a service channel, and it is the part businesses most often underuse. A customer asking whether a size is available does not want a template. They want an answer from someone who checked. The window exists precisely to permit that, and a business that answers every inbound message with a stiff pre-approved format is declining a capability it already has.
One caveat on cost, because it is changing shortly. Free-form replies inside the window have not carried a charge, which is a large part of why keeping conversations alive has been such good economics. Meta has announced that from 1 October 2026 service messages and utility templates sent inside the window stop being free. The window's behaviour is not changing on that date — only its billing status — so the right response is to know your own monthly volume of in-window replies, not to start rationing them in advance of a rate nobody has published.
Outside the window: templates, and nothing else
Once 24 hours have passed since the customer's last message, the window closes and free-form messaging stops working. A business wanting to reach that person again must send an approved template. This is the single most common source of the complaint that a message "didn't send" — the send was refused because the window had shut, not because of a technical fault.
The practical consequence is that anything a business might need to say outside a live conversation has to be anticipated and approved in advance. Order confirmations, delivery updates, appointment reminders and one-time passcodes all exist as templates because they are exactly the messages that need to go out when the customer is not currently chatting. A business that has not thought about which of its outbound messages fall into this bucket discovers the gap at the worst possible moment.
Sending a template also does not reopen a free-form window. Only an inbound message from the customer does that. So a template is best drafted to invite a reply, because the reply is what restores the ability to talk normally. A confirmation that ends with a genuine reason to respond converts into a live conversation; one that closes the topic leaves the business back outside the window for its next message.
Designing around the window rather than fighting it
Once the mechanics are clear, some sensible operational habits follow. Reply while the window is open, because a reply sent within minutes is a plain message and one sent two days later requires an approved template and a fresh approach. This is the concrete, mechanical reason speed matters on this channel, quite apart from any argument about customer expectations.
Build the templates you will actually need before you need them, and choose their categories honestly. A business that waits until a window has closed to discover it has no suitable approved template has a review cycle standing between it and the customer.
Measure whether inbound conversations are being answered inside the window at all. This is a more useful operational number than a raw count of messages sent, because it tracks the thing that determines whether the cheap, flexible, high-quality version of the channel is being used. A business with many open windows and few replies inside them is paying for templates to do work that free-form conversation would have done better.
The mechanics worth remembering
Three facts carry most of the practical weight. The window is opened by the customer, not the business, and any inbound message from them resets it for a further 24 hours. Inside the window, free-form replies work. Outside it, only approved templates are delivered, and a template does not itself reopen the window — only a reply from the customer does.
Everything else about business messaging on WhatsApp is easier to reason about once those three are internalised. Why templates need approval at all, why marketing requires consent, why reply speed is treated as an operational discipline rather than a nicety, why a business cannot simply import a list and start chatting: each is a consequence of the same underlying design.
The billing details layered on top will keep moving, and the 1 October 2026 change to in-window charging is a live example of that. The structure underneath has been stable, and it is the part worth building a process around. Check Meta's own documentation for the current rate on the day it matters, and treat the window itself as the fixed thing it has been.
Common questions
Does sending an approved template open the 24-hour window?
No. Only an inbound message from the customer opens or resets the window. A template can be delivered outside the window, but sending one does not restore your ability to send free-form messages. If the recipient replies to your template, that reply opens the window — which is why a template that invites a genuine response is more useful than one that closes the subject.
The customer messaged me three days ago. Why can't I just reply?
Because the window closed 24 hours after their last message. A free-form reply will be refused. To reach them now you need an approved template, and if what you want to say is promotional, you also need marketing consent from that person. This is the usual explanation behind a message that appears not to send with no obvious technical error.
If a customer keeps replying, does the window keep extending?
Yes. Every inbound message from that customer resets the 24-hour clock, so an active conversation renews itself for as long as they keep participating. The window is tracked per customer, so an open window with one person tells you nothing about your ability to message anyone else.
Should I stop replying inside the window before the October 2026 billing change?
No. The window's behaviour is not changing on 1 October 2026 — only the billing status of service messages and in-window utility templates. Cutting off free-form replies early gives up a real customer-service capability against a charge that has not taken effect and a rate that was not public at the time of writing. Measure your current monthly in-window volume instead, so you can price the change when the rate card lands.