How to Send Automatic Booking Reminders (Step-By-Step)

What you'll build: An automation that watches for new Calendly bookings and automatically texts the client a reminder one hour before their appointment. No manual texting, no missed appointments.

What you'll learn: How to calculate a time in the past relative to a booking, how to delay a Zap until that exact moment, and how to send a real SMS through Twilio.

This one is marked Intermediate because it chains four steps together instead of two. You'll need a free Zapier account, a Calendly account, and a Twilio account (Twilio requires buying a phone number to send SMS from. This typically costs a small monthly fee, but the first message is usually covered by free trial credit).

Step 1: Create the Zap and connect Calendly

1. Go to zapier.com, log in, click Create, then Zaps.
2. Click the 1. Trigger box, search for Calendly, and select it.
3. Under Event, choose Invitee Created, then click Continue.
4. Sign in to your Calendly account. Click Continue.
5. Under Event Type, select a specific event type or leave it on any. Click Continue.
6. Click Test trigger. Confirm a real booking appears with a name, phone number, and appointment time, then click Continue.

If no phone number appears in the test data, your Calendly booking form isn't currently collecting one. Add a phone number question to the booking form before continuing.

Step 2: Calculate "1 hour before" with Formatter

Zapier doesn't know "1 hour before the appointment" on its own, you have to calculate that exact time first.

1. Click + to add a step. Search for Formatter by Zapier and select it.
2. Under Event, choose Date / Time, then Continue.
3. Under Transform, choose Add/Subtract Time.
4. In the Date field, use the insert-data icon to select the appointment start time from your Step 1 Calendly data.
5. Set Value to 1 and Unit to Hours, and set the sign to subtract (check the transform's direction option, you want the result to land before the appointment, not after).
6. Click Continue, then Test step. Confirm the output time is exactly one hour earlier than the real appointment time from Step 1.

Step 3: Delay until that exact time

1. Click +. Search for Delay by Zapier and select it.
2. Under Event, choose Delay Until, then click Continue.
3. In the Date/Time field, use the insert-data icon to select the calculated time from Step 2, not the raw appointment time from Step 1.
4. Click Continue. This step has nothing to test live since it's a wait. Zapier will confirm the setup and move on.

Step 4: Send the SMS with Twilio

1. Click +. Search for Twilio and select it.
2. Under Event, choose Send SMS, then click Continue.
3. Sign in with your Twilio Account SID and Auth Token, both found on your Twilio console dashboard. Click Continue.
4. Under From, select the phone number you purchased in Twilio.
5. Under To, use the insert-data icon to select the phone number field from your Step 1 Calendly data.
6. In the Message Body, build a message with real fields, for example: Hi [Name from Step 1], reminder: your appointment is in 1 hour at [Time from Step 1]. See you soon!
7. Click Continue, then Test step. Check the actual phone number for the test text.

Step 5: Turn it on

1. Click Publish, then toggle the Zap to On.
2. Book one real test appointment far enough in the future to confirm the reminder text arrives roughly an hour before it, right on schedule.

Common mistakes

• Skipping the Formatter step and connecting the Delay directly to the raw appointment time. This sends the reminder the moment the booking happens, not before the appointment.
• Trying to send SMS from a personal number instead of a number purchased through Twilio. Twilio requires its own registered number.
• Not collecting a phone number on the Calendly booking form, so Step 1 has nothing to work with.
• Testing only with an appointment booked minutes away, meaning you never actually see the full delay behavior play out.
• Forgetting international phone number formatting. Twilio expects numbers in a full international format, not just local digits.

Your first step

• Confirm your Calendly booking form collects a phone number.
• Buy a phone number in Twilio if you don't have one yet.
• Build the four-step Zap: Calendly trigger, Formatter subtract-time, Delay Until, Twilio Send SMS.
• Test each step individually before publishing.
• Book one real future appointment and confirm the reminder arrives on time.

Continue learning

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