Multiply the hours saved by what an hour of that person's time costs you. Include employer costs, such as National Insurance and pension contributions, not just the hourly wage. For reference, the National Living Wage for workers aged 21 and over is £12.71 an hour from April 2026, and the ONS puts median weekly earnings for full-time employees at £811.20 in April 2026.
Here is a made-up example to show the sum. Say a tool saves five hours a week, and an hour of that person's time costs you £15 including employer costs. That is £75 a week, or about £325 a month. If the tool and the time spent checking it cost £120 a month, the saving is clear. If they cost £300, it is marginal.
Be honest about what happens to the saved time. If the hours go into calling back leads or serving more customers, they have real value. If they disappear into other admin, the saving is smaller than it looks on paper.
Owners often forget their own time. If AI saves you two evenings of emails a week, that has value too, even if it never shows up in the accounts.