How Much Does It Cost to Build a Booking App?

The headline number hides one variable that swings the budget more than anything else: how hard your availability logic has to work. A single resource on one timezone with fixed slots sits near the €5,000 floor. The moment you add overlapping resources, buffer times between bookings, variable durations, or timezone-aware slots, you are paying for conflict-resolution code that has to be correct every time — a double-booking is a refund and a lost customer, so it gets tested hard.

The other big movers:

• Calendar sync — one-way export (.ics feed) is cheap. Bidirectional sync with Google Calendar or iCal, where an external edit has to free up your slot without losing data, is where hours pile up. On BookBed I run bidirectional iCal sync across multiple properties with zero double-bookings over hundreds of reservations — that reliability is the part that costs real time to build.
• Payments — a flat charge at booking is simple. Deposits, partial payments, and refund/cancellation policies each add a state to track.
• Notifications — email confirmations are baseline. SMS reminders, reschedule links, and cancellation flows each add scope and a third-party bill.

To land near €5,000–8,000, cut to one booking path that works:

• One resource type, fixed-length slots, one timezone.
• Email-only notifications (no SMS).
• A single Stripe charge at booking — skip deposits and partial payments for v1.
• One-way calendar export instead of bidirectional sync.
• A simple admin view to manage slots and see bookings.

That is a real, shippable product. You can add the rest once bookings are actually coming in.

What pushes you toward €12,000–18,000: bidirectional calendar sync, multi-resource availability with buffers, deposits plus refund policies, SMS reminders, and a reporting-heavy admin dashboard. None of these are wasted money — but adding all of them to v1 is the most common way a €6,000 build becomes an €18,000 one before a single customer has booked. Sequence them.

Even the high end stays well under the €30,000–90,000 agency range, mostly because there is no account-management or handoff layer between you and the person writing the code — and the work ships without the overhead of the typical agency timeline.

The build quote is not the whole bill. Budget for these from day one:

• Third-party / SaaS fees — Stripe takes roughly 1.5%–3% + a fixed fee per transaction, so payments scale with revenue, not the build. SMS (Twilio or similar) is per-message; transactional email has a free tier that you outgrow as volume rises.
• App-store costs — only relevant if you go native. Apple charges $99/year, Google a one-time $25, plus review cycles on every update. A mobile-friendly web app skips all of it, which is why most booking products start there.
• Ongoing hosting — a Firebase or Supabase backend is often free-to-cheap at low volume and rises with usage. Plan for it to grow, not stay flat.
• Maintenance — dependency updates, OS/browser changes, and small fixes are real recurring work. A rough rule is 15–20% of the build cost per year to keep things current. A booking app that quietly stops sending confirmation emails is worse than no app, so this is not optional.

For a booking app, fixed-scope is the safer default. The feature set is well understood, so it can be specced precisely — you know what a booking flow, an availability engine, and a payment step involve before writing code. Fixed-scope puts the estimation risk on the developer, not you, and that is the right place for it. Hourly only makes sense for the genuinely undefined parts: an unusual integration, or a sync against an API nobody has touched yet. A clean split is fixed-price for the core build, hourly for a named list of unknowns.

On timeline, plan for 5 to 12 weeks end to end. The lean v1 above lands near the 5-week mark; the full feature set with bidirectional sync, deposits, and SMS runs closer to 12 weeks. Anyone promising a complex booking system in two weeks is cutting the testing that keeps double-bookings from happening — which is the one thing this kind of app cannot get wrong. I have shipped this pattern in production (BookBed for multi-property booking, Callidus for clinic scheduling on React + Firebase), and the realistic path is steady weeks, not a sprint.