How to send automatic birthday messages to your customers with n8n and AI

A birthday message is one of the few emails customers almost always open, and it doesn't feel like advertising. For a hair salon, a garage, a clinic or a small shop, it's a natural reason to remind people you exist and, with a small gift (10% off or a free coffee), win a visit that same month. The hard part is remembering who has a birthday every single day.

In this guide you'll build an n8n workflow that every morning checks your customer list in Google Sheets, finds who has a birthday today, writes a short personal greeting with AI and sends it via Gmail (or WhatsApp) with a gift code, without double-sending or messaging anyone who opted out.

What you'll build

A five-step workflow that runs on its own every day:

Daily trigger: a Schedule Trigger node runs at 9:00.
Read customers: the Google Sheets node reads your "Customers" sheet.
Birthday filter: a Code node keeps only those whose birthday is today, who gave consent and who haven't been greeted this year.
AI greeting: a Basic LLM Chain node writes a short message with the customer's name and last service.
Send and log: Gmail sends the message and Google Sheets writes the year in the greeted column.

What you need

An n8n instance (cloud or installed free on your computer).
Google Sheets and Gmail connected in n8n (or WhatsApp Cloud API if your customers prefer WhatsApp).
An OpenAI (or other AI provider) API key with a monthly spending limit set in its dashboard.
A "Customers" sheet with these columns: name, email, birthday (format DD-MM, no year), last_service, consent (yes/no) and greeted (empty).

Step 1: prepare the customer sheet

Store only the day and month: you don't need the year or age, so you collect less personal data. Ask for the date when the customer signs up (for example in your new-client welcome flow) and explain what it's for. The consent column matters: in the EU and UK you need permission to send marketing messages, and a discount code counts as one.

Step 2: trigger and read

Add a daily Schedule Trigger at 9:00 (check the workflow time zone under Settings). Connect it to Google Sheets → Get Row(s) pointing to your "Customers" sheet.

Step 3: filter today's birthdays

Add a Code node (Run Once for All Items) with this code:

const today = new Date();
const dd = String(today.getDate()).padStart(2, '0');
const mm = String(today.getMonth() + 1).padStart(2, '0');
const year = String(today.getFullYear());
return $input.all().filter(i => {
  const c = i.json;
  return String(c.birthday).trim() === `${dd}-${mm}`
    && String(c.consent).toLowerCase() === 'yes'
    && String(c.greeted) !== year
    && c.email;
});

If nobody has a birthday today, the node returns nothing and the workflow stops without spending a cent on AI. Tip: store 29 February birthdays as 28-02.

Step 4: write the greeting with AI

Add a Basic LLM Chain with a small, cheap model (for example gpt-4o-mini) and this prompt:

You work at [BUSINESS NAME]. Write a birthday message for {{ $json.name }},
whose last visit was for: {{ $json.last_service }}.
- Max 4 sentences, warm and natural, in English.
- Mention the gift: 10% off this month with code BDAY10.
- Don't invent facts, avoid emoji overload and ad-speak.
Return only the message text.

Mentioning the last service ("fancy another autumn colour?") is what stops it feeling like a mass mailing.

Step 5: send and mark as greeted

Connect a Gmail → Send node with the subject Happy birthday, {{ $('Code').item.json.name }}! and the AI text as the body. Then a Google Sheets → Update Row node that matches on email and writes the current year in greeted. That way, even if the workflow runs twice in a day, nobody gets two greetings.

If you use WhatsApp, remember that outside the 24-hour window Meta only allows approved templates: create a marketing template with the name as a variable.

How to test it

Add a row with your own email, today's date in birthday and yes in consent.
Run the workflow manually and check that the greeting arrives and greeted gets filled in.
Run it again: nothing should be sent this time.
Set consent to no on another test row and confirm it's skipped.

Cost and best practices

Cost: each greeting costs less than a tenth of a cent in AI API usage. With 500 customers that's fewer than 2 messages a day.
Measure results: use a dedicated discount code (BDAY10) to see how many visits it brings. You can track it in your daily AI summary report.
Get error alerts: set up an error workflow so you hear if Gmail or the sheet fails, as covered in n8n error handling.
Combine it with your campaign to win back inactive customers: a birthday is the perfect moment to bring back someone you haven't seen in months.

Start with ready-to-import templates

If you want your customer-service base in n8n already built, download the free WhatsApp agent or check out the full AgentKiosk pack: 8 tested agents in English and Spanish, each with workflow, prompt and guide, ready to import and pair with this automatic birthday flow.