When businesses try to quantify the cost of IT downtime, they usually start with staff hours. If 15 people can't work for two hours, that's 30 staff-hours lost. At an average fully-loaded cost of £25 per hour, that's £750. Manageable.
The problem is that the direct staff cost is only one part of the number, and often not the largest part.
The Components of Downtime Cost
Direct labour cost is the lost productive time for staff who can't work. For knowledge workers heavily dependent on IT systems, this is close to 100% of their time during the outage. For staff with non-IT-dependent work they can switch to, it's lower.
Management time during the incident — diagnosing the problem, communicating with staff, escalating to IT support, managing client impacts — is often significant. A two-hour technical outage may involve four hours of senior management attention spread across the organisation.
Revenue impact is harder to quantify but often larger than the labour cost. Missed orders, delayed customer responses, SLA breaches, and sales opportunities not progressed during the outage all represent lost revenue. For e-commerce businesses or businesses handling inbound sales enquiries, the revenue impact of downtime is direct and immediate.
Recovery costs include IT support time, data recovery work, and any hardware or software costs associated with fixing the root cause.
Reputational impact is the hardest to quantify and the longest lasting. A client who couldn't reach you during an outage, or who received a delayed or wrong order because of an IT failure, may not complain — they may simply not come back.
Calculating Your Number
A simple framework for estimating downtime cost per hour:
Take your annual revenue. Divide by the number of working hours in the year (roughly 2,000 for a standard working year). That gives you revenue per hour. Multiply by the percentage of revenue that depends on IT systems being operational — for most service businesses, that's 80-100%.
For a business with £1.5m turnover where 90% of activity requires IT: that's roughly £1.5m × 0.9 / 2,000 = £675 per hour, before staff costs or recovery costs.
At that number, a four-hour outage costs around £2,700 in lost revenue alone — before you count staff time, IT support costs, or the client who took their next order elsewhere.
What This Changes
Most businesses invest in IT based on purchase cost and convenience, not total cost of ownership including downtime risk. When downtime has a realistic figure attached to it, the investment case for redundancy, better backup, proactive monitoring, and faster support response times looks very different.
A failover internet connection costs £40-80 per month. If your business loses £500 per hour when the internet goes down, the payback time on a failover connection is measured in hours of downtime per year. For most businesses, that's a trivially easy justification.
Similarly, the premium for same-business-day hardware replacement on a critical server or the cost of a UPS for your network equipment looks very different against a realistic downtime cost figure.
The businesses I see making good IT investment decisions are the ones that have actually done this calculation. The ones making poor decisions are managing IT purely on visible cost.