WhatsApp vs SMS for appointment reminders: which is better?
By Marai ·
If you are looking for a way to send automatic reminders to your clients, you have probably come across two main options: SMS and WhatsApp. Many scheduling platforms offer SMS. Some offer WhatsApp. Few clearly explain which one suits you best and why.
Let us compare both channels on what actually matters for a service business.
Open rate: the metric that decides everything
There is no point sending a reminder if the client does not read it. And here the difference between SMS and WhatsApp is significant.
SMS
SMS has historically had a high open rate, around 90–95 %. However, this figure is misleading: many users open an SMS without actually reading it carefully, especially because SMS has become associated in recent years with advertising, verification codes, and banking alerts. A legitimate business SMS competes for attention with dozens of marketing messages.
Moreover, on many Android devices, SMS messages from businesses end up in a separate folder that the user does not actively check.
WhatsApp has open rates very similar to or higher than SMS, but with one fundamental difference: context. WhatsApp is the primary messaging app for the vast majority of people in Spain. Messages are read on the same screen where they chat with friends and family, which means real attention — not just “open and close”.
A reminder that arrives via WhatsApp is far more likely to be read, understood, and acted upon.
Cost per message
SMS
The cost of an SMS in Spain ranges between €0.04 and €0.09 per message, depending on the provider and volume. That may not seem like much, but consider the maths:
- 20 appointments a day × 2 reminders = 40 SMS per day
- 40 SMS × €0.06 = €2.40 per day
- Per month: around €50–70, just for reminders
And that cost applies per send, regardless of whether the client reads the message or not.
WhatsApp (Business API)
WhatsApp Business API conversations are priced per conversation (not per individual message). In Spain, a service conversation (initiated by the business) costs approximately €0.04–0.08 and covers all messages exchanged within a 24-hour period.
This means that if you send a reminder and the client replies to confirm, all of that counts as a single conversation. With SMS, each message in each direction is charged separately.
Interaction: one-way messages vs conversation
SMS
SMS is fundamentally one-directional. You can send a reminder, but if the client replies, handling that response is complicated and expensive. Most platforms that offer SMS for reminders do not process replies, or do so in a very limited way.
Result: you send “Remember your appointment tomorrow at 10:00” and the client has no easy way to reply “I cannot make it — can you change it to Thursday?”.
WhatsApp is conversational by nature. The client can reply directly to the reminder, confirm the appointment, cancel, or ask a question. If you have a chatbot connected, those replies are processed automatically. If not, they at least arrive in the business inbox for someone to handle.
This two-way interaction capability turns the reminder into an active management tool, not just a passive notification.
Rich content
SMS
SMS is limited to 160 characters of plain text (or 70 if you use special characters like accented letters or other non-GSM characters, which take up more space in GSM encoding). It does not support images, buttons, formatted clickable links, or any kind of rich content.
For a basic reminder it may be enough, but if you want to include a cancellation link, a confirmation button, or the business address with a Google Maps link, SMS falls short. With an online calendar, WhatsApp reminders include interactive confirm and cancel buttons.
WhatsApp supports long messages, emojis, links with preview, images, documents, location sharing, and even interactive buttons (in API templates). A WhatsApp reminder can include:
- All appointment details without any character limit
- A “Confirm” button and a “Cancel” button
- The exact business location with a map link
- A link to reschedule online
That richness of content is not a cosmetic feature — every element reduces friction for the client to take action.
Penetration in Spain: the decisive factor
This is where the comparison tilts decisively. In Spain, WhatsApp has an estimated penetration of over 95 % among smartphone users. It is the default messaging app. It is not just another app — it is the communication app.
SMS, on the other hand, has lost relevance as a personal communication channel. Most users now associate it with verification codes, banking alerts, and advertising. It is not a channel users actively check or feel comfortable interacting with.
This has a clear practical consequence: a WhatsApp reminder is perceived as natural, expected communication. An SMS from a business is perceived, at best, as a functional notification and, at worst, as spam.
What about email?
It is worth mentioning email as a third channel. It does not replace WhatsApp or SMS for urgent reminders (email is read with less immediacy), but it has its own advantages:
- Zero cost on most platforms
- No restrictions on templates or approvals
- Ideal for booking confirmations that the client can search for later in their inbox
- A perfect complement to WhatsApp as a second channel
The most effective combination for most businesses in Spain is WhatsApp as the primary channel + email as a backup. SMS remains a third option for the few clients who do not use WhatsApp.
Delivery reliability
SMS
SMS has a historical advantage: it works without an internet connection — only mobile coverage is needed. This makes it more reliable in areas with poor internet connectivity or for users with very basic phones.
However, in practice this advantage is increasingly irrelevant. 4G/5G coverage in Spain is extensive and the vast majority of users have a smartphone with mobile data.
WhatsApp requires an internet connection, but given that almost all smartphones in Spain have permanent mobile data, delivery is practically guaranteed. WhatsApp also handles deferred delivery automatically: if the user is offline when the message is sent, they receive it as soon as they reconnect.
WhatsApp also provides delivery confirmation (double tick) and read confirmation (blue double tick), something standard SMS does not provide reliably.
Summary table
| Criterion | SMS | |
|---|---|---|
| Open rate | High, but superficial reading | Very high, with genuine attention |
| Cost per message | €0.04–0.09 per SMS | €0.04–0.08 per conversation (24h) |
| Interaction | One-directional | Two-directional, conversational |
| Content | 160 characters, plain text | No limit, buttons, images, location |
| Penetration in Spain | Universal (but declining channel) | 95 %+ (preferred channel) |
| User perception | Notification / spam | Natural communication |
| Offline delivery | Yes (mobile coverage only) | Yes (when internet reconnects) |
The decision for your business
If your business is in Spain and your clients are smartphone users (which is practically everyone), WhatsApp is the most effective channel for appointment reminders. It offers better real read rates, allows interaction, supports rich content, and is perceived as natural communication — not spam.
SMS has its place in very specific scenarios: older clients without smartphones or markets where WhatsApp is not dominant. But for the Spanish market in 2026, WhatsApp combined with email covers virtually every use case.
At Marai we have made this decision: we offer reminders via WhatsApp and email, not SMS. Email reminders are included on all plans (including the free plan). WhatsApp reminders are available from the Starter plan with the WhatsApp Business connection. If you want to explore all the reminder options, visit the automatic reminders section.