Measure the annual trade
Suppose a five-day pattern pays £32,000 take-home and a four-day reduced-hours pattern pays £28,000. The visible annual price of the change is £4,000. If weekly paid hours fall from 37.5 to 30 across 46 working weeks, 345 paid hours are returned.
Income given up per hour returned = annual take-home reduction ÷ annual paid hours returnedThis does not mean an hour of your life is objectively worth £11.59. It means the proposed arrangement exchanges £11.59 of annual take-home income for each paid working hour removed, before considering commuting and other effects.
Add the journey that disappears
If moving to four days removes one £12 commute for 46 weeks, the direct travel saving is £552. The practical cash sacrifice is then closer to £3,448 before any other cost changes. If the fifth day also requires childcare or parking, include those only where they genuinely disappear.
Compressed hours need a different interpretation
If the four-day option keeps 37.5 weekly hours, you have not bought back 345 paid hours. You have reorganised the same paid workload into longer days. The benefit may still be valuable because one attendance day disappears, but the calculation is then about commuting and calendar flexibility rather than fewer paid hours.
Test the result with and without savings
Continuing the example, the raw take-home reduction is £4,000. Removing a £12 weekly commute across 46 weeks saves £552, reducing the cash sacrifice to £3,448. If the removed working day also avoids £20 of childcare for those same 46 weeks, another £920 is saved and the net cash sacrifice falls to £2,528.
| Scenario | Annual cash sacrifice | Per returned paid hour |
|---|---|---|
| Pay change only | £4,000 | £11.59 |
| After commute saving | £3,448 | £9.99 |
| After commute + childcare saving | £2,528 | £7.33 |
This sensitivity check shows why two people offered the same salary reduction can reach very different conclusions: the costs that disappear with the fifth day can materially change the exchange.
What the number cannot decide
- whether longer or shorter days fit your energy and family routine;
- whether reduced income affects borrowing, pension saving or other commitments;
- whether workload expectations fall with contracted hours;
- whether the employer can change the arrangement later.