Compare the change, not the whole job
If the proposed role adds two office days each week, calculate the two additional journeys rather than charging the new role for commuting you already do. The same principle applies to pay: use the increase you reasonably expect to keep, not the full salary.
Extra commute cost/year = extra office days/week × working weeks × round-trip cost/dayExtra commute hours/year = extra office days/week × working weeks × round-trip minutes/day ÷ 60Worked example
Suppose a new role increases expected annual take-home pay by £4,200. It requires two extra office days per week, the extra round trip costs £14, takes 70 minutes and you expect 46 working weeks.
Ignoring the value of personal time, the cash gain after the extra travel cost is £2,912. If you choose to test a personal-time value of £10/hour, the 107.3 hours represent another £1,073 comparison cost, leaving £1,839 of the original £4,200 increase. Setting time to £0 is equally valid when you only want a cash comparison.
Why a time value is optional
Your free time does not have a universal market price. Giving it a value is simply a scenario tool: it lets you ask how the decision looks if an additional hour in traffic matters to you financially. Try several values rather than treating one figure as objectively correct.
Calculate the minimum increase needed to break even
You can reverse the comparison and ask how much extra take-home pay would be needed simply to cover the new commute. With £1,288 of extra annual travel cost and no time value, the cash break-even increase is £1,288. At a £10/hour time scenario, add £1,073 for the 107.3 extra hours, giving an illustrative break-even increase of £2,361.
Break-even take-home increase = extra annual travel cost + (extra commute hours × chosen time value)If the actual pay increase is only slightly above that threshold, the result is sensitive to small changes in attendance, fares, fuel or journey time. Testing a low, central and high commuting scenario is more useful than relying on one optimistic journey.
Costs people often miss
- parking or station charges;
- fuel or public-transport price differences;
- additional childcare created by longer days;
- extra meals or convenience spending;
- the possibility that attendance expectations increase later.
Income tax depends on personal circumstances. Work Decisions deliberately asks for the change you expect to keep rather than embedding a generic tax result.