The verdict in three sentences
For a London headquarters of 500 to 800 employees moving to 0.7 desks per person, a booking SaaS at 3 to 8 GBP per user per month is enough as long as your rules stay standard. Once you need to combine Microsoft 365 calendars, access control badges and team rules (anchor days, neighbourhoods, accessible desks), a custom app at 50,000 to 120,000 GBP pays back in 3 to 5 years. The real financial lever is property: 20 to 30% of floor space handed back, worth hundreds of thousands of pounds of rent per year in central London.
SaaS or custom build: what each option costs in 2026
The desk booking market is mature. Vendors cover desks, rooms and parking, with a mobile app and an Outlook or Teams add-in. A custom build makes sense when hybrid working becomes a real estate steering tool, connected to HR data and sensors.
| Cost item (2026 ballpark) | Booking SaaS | Custom app |
|---|---|---|
| Setup | 2,000 to 10,000 GBP | 50,000 to 120,000 GBP |
| Subscription for 600 users | 21,600 to 57,600 GBP per year | 0 (hosting 3,000 to 8,000 GBP per year) |
| Microsoft 365 integration (Outlook, Teams) | Standard, often included | Custom, free business rules |
| Access control link (badges) | Limited connectors, add-on | Direct integration, automatic check-in |
| Team and neighbourhood rules | Bounded configuration | Free logic (zones, quotas, priorities) |
| Ownership of occupancy data | Vendor side | Yours, usable in BI |
| Ongoing maintenance | Included in subscription | 12,000 to 22,000 GBP per year |
Over 5 years, for 600 users, a SaaS costs 110,000 to 300,000 GBP. A custom app lands around 120,000 to 260,000 GBP including maintenance. The gap depends mainly on the negotiated per-user price and how many specific features you need.
Sensors, badges, Microsoft 365: the budget for measuring occupancy
A booking does not prove occupancy. Workplace studies regularly find 15 to 25% ghost bookings. Reliable figures combine three sources: check-in (QR code or badge), under-desk occupancy sensors and Wi-Fi data.
| Component | 2026 unit cost (estimate) | For 420 desks | Measurement reliability |
|---|---|---|---|
| QR code check-in on the desk | 2 to 5 GBP per label | 1,000 to 2,000 GBP | Medium (frequent omissions) |
| Badge check-in at the turnstile | Development 6,000 to 15,000 GBP | 6,000 to 15,000 GBP | Good at floor level |
| Under-desk occupancy sensor | 70 to 180 GBP per desk | 29,400 to 75,600 GBP | Very good |
| Sensor platform subscription | 2 to 5 GBP per sensor per month | 10,000 to 25,000 GBP per year | Depends on vendor |
| Anonymised Wi-Fi counting | Licence 5,000 to 12,000 GBP per year | 5,000 to 12,000 GBP | Good per zone |
| Automatic release without check-in | Included in the app | 0 | Removes ghost bookings |
Rule of thumb: start with badge check-in and automatic release after 30 minutes, then fit sensors on one pilot floor. Under UK GDPR, data must be aggregated by zone, and employees must be informed (with a DPIA) before any sensor rollout.
What the specification must include
A solid specification prevents 80% of budget drift. It should state:
- the target ratio (0.7 desks per employee) and team rules (anchor days, zones per department);
- single sign-on with Microsoft Entra ID and Outlook room sync;
- the connector to your access control system and its export format;
- dashboards: occupancy rate by day and floor, Tuesday and Thursday peaks;
- WCAG 2.2 AA accessibility for the app and the lobby screen;
- hosting in the UK or the European Union.
Allow 10 to 14 weeks from scoping to going live on a first floor, then 4 to 6 weeks to roll out.
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Mini case study
Emma, head of workplace at a 600-employee headquarters in the City of London, occupies 60,000 sq ft at 85 GBP per sq ft per year all-in. Moving to 0.7 desks per employee lets her hand back a floor of 15,000 sq ft, that is 1,275,000 GBP of annual rent saved. She compares a SaaS at 5 GBP per user (36,000 GBP per year) with a custom app at 85,000 GBP plus 16,000 GBP yearly maintenance and sensors on 420 desks for 45,000 GBP. Over 5 years, the custom option costs 210,000 GBP, the SaaS 180,000 GBP plus 25,000 GBP of connectors. At a similar cost, she chooses custom to own occupancy data and team rules. The project represents less than 4% of the property savings over the period.
FAQ
How much does a custom desk booking app cost in London?
Expect 50,000 to 120,000 GBP depending on integrations (Microsoft 365, access control, sensors). Ongoing maintenance adds 12,000 to 22,000 GBP per year.
What desk ratio should a hybrid office target?
Most headquarters target 0.6 to 0.8 desks per employee depending on remote days. At 0.7 with 2 remote days a week, peak occupancy stays around 85%.
Do we need occupancy sensors?
Not at first: badge check-in is often enough. Sensors at 70 to 180 GBP per desk are justified when you are deciding on a space reduction of 10,000 sq ft or more.
Do employees need to be consulted?
Yes, sensors process personal data and require a DPIA and clear employee information. Allow 1 to 2 months for this, alongside any works council or union consultation.
How fast can the app be delivered?
A one-floor pilot goes live in 10 to 14 weeks. Full rollout across a 600-person headquarters takes another 4 to 6 weeks.
Let's scope your project. Send us your headcount, target ratio and tools (Microsoft 365, badges) and we will price the scope, indicative budget and timeline of a pilot. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
