Online booking sounds simple. Let people pick a time, add their details, done. Then you start building it and the questions pile up. What happens with no-shows? Should you take a deposit? Which calendar is the source of truth? What if two people book the same slot a second apart?

We have built booking into salons, clinics, studios, and trades sites. The pattern is always the same: the hard part is not the calendar widget, it is the rules around it. Here is what to think through before you commit.

Decide what you are actually booking

A booking system for a barber is not the same as one for a physiotherapy clinic or a holiday cottage. Get specific early.

Ask yourself:

• Is it a fixed slot (a 30 minute appointment) or a range (a two night stay)?
• Does the service length vary by what the customer picks?
• Do you need to assign a specific staff member, or any available one?
• Are there resources beyond people, such as a room or a piece of equipment?
• Can one booking include multiple services back to back?

These answers shape everything. A "book a haircut" flow is a weekend of work. A "book a 90 minute treatment with a named therapist in a specific room, with buffer time for cleaning" flow is a proper project.

Off the shelf or custom

For many businesses, a tool like Calendly, Cal.com, or a sector-specific system (Fresha, Treatwell, SimplyBook) will do the job for a monthly fee. If your rules are standard, use one. There is no prize for rebuilding what already works.

You want custom when:

• Your booking logic is unusual and the off the shelf tools fight you.
• Booking needs to feed into other parts of your site or back office.
• The branding and flow matter enough that an embedded third-party widget feels wrong.
• You are paying per-booking fees that have grown past the cost of owning the thing.

We tend to recommend starting with a hosted tool and only building custom when you hit a real wall. If you are weighing this up, our web apps service is where that conversation usually lands.

Plan for no-shows before launch

No-shows are the quiet killer of a booking system. A fully booked diary that half empties on the day is worse than no system at all, because you turned other people away.

Three levers work:

Deposits or full prepayment. The strongest deterrent. Even a small deposit changes behaviour. Decide whether it is refundable and up to what point.

Reminders. An email the day before and a text a few hours before cuts no-shows noticeably. Build these in from day one, not as a later add-on.

A clear cancellation window. "Cancel at least 24 hours before" only works if the system enforces it and the customer saw it when they booked.

If you take payment, you are now handling card data flows and refunds. Use Stripe or a similar provider and never store card details yourself.

Calendar sync and the single source of truth

This is where most DIY setups come undone. If your bookings live in one place and your staff keep their own Google Calendars, double bookings are a matter of time.

Pick one source of truth. Usually that is the booking system itself. Then sync outward to staff calendars, not inward. If a staff member blocks personal time, that block needs to feed back and close those slots. Two-way sync is harder than one-way, so be honest about whether you need it.

Also think about timezones if you serve customers outside the UK. A video consultation booked from abroad at "2pm" needs to be unambiguous about whose 2pm it is.

Handle the race condition

Two people land on the last Saturday slot at the same moment. Both click book. What happens?

A proper system locks the slot the instant one booking confirms and shows the other person a clear "sorry, just taken" message. A weak system confirms both and leaves you to grovel by phone. If you go custom, ask your developer directly how they prevent double bookings under load. It is a basic test of whether they have done this before.

Keep the form short

Every extra field loses people. Name, contact, service, time. That is often all you need up front. Collect anything else after the booking is confirmed, or at the appointment.

Phone number matters if you send text reminders. Make clear why you are asking. A booking abandoned halfway is a customer who went to a competitor whose form was one step shorter.

Make it work on a phone

Most bookings now happen on mobile, often in a spare two minutes. If the date picker is fiddly or the slots are hard to tap, people give up. Test the whole flow on a real phone, on real mobile data, not just on your desktop at full broadband.

Confirmation and what comes after

The moment of booking is the start, not the end. A good flow sends:

• An instant confirmation email with the details and an add-to-calendar link.
• A reminder before the appointment.
• A way to reschedule or cancel without ringing you.
• A follow-up afterwards, which is a natural moment to ask for a review.

That last one quietly builds your reputation. We have written before about why those reviews are worth chasing in Google reviews for business.

Where booking should live on your site

Do not bury it. The booking button should be visible on every page, in the header, and repeated at the end of each service description. If someone reads about your treatment, the next thing they want is a way to book it, right there, without hunting.

For local businesses, link booking from your Google Business Profile too. Someone who finds you on Maps should be able to book without even visiting the homepage.

Start simple, then grow

The temptation is to spec every rule, every edge case, every staff preference before launch. Resist it. Launch with the core flow for your most common booking, watch how real customers use it, then add complexity where it earns its place.

A booking system you ship this month and refine beats a perfect one still in planning next spring. Get the money rules right, keep the form short, make it fast on a phone, and the rest is iteration.

Ruben, Founder