1. Calculate the contractual overtime pay
Use the base rate and multiplier in your contract or employer policy. There is no universal UK overtime multiplier, so do not assume time-and-a-half unless that is actually your rate.
Total overtime pay = base hourly rate × overtime multiplier × overtime hoursPremium extra = base hourly rate × (multiplier − 1) × overtime hoursAt £15/hour, six hours paid at 1.5× produce £135 gross overtime pay. Six ordinary hours at £15 would be £90, so the enhanced premium is £45.
2. Subtract the costs created by accepting the shift
A gross-pay result does not show whether the shift is worthwhile for you. Add only incremental costs caused by working it: extra travel, childcare, parking, food or other unavoidable spending.
| Illustrative item | Amount |
|---|---|
| Gross overtime pay | £135 |
| Extra travel | −£12 |
| Extra childcare | −£28 |
| Other incremental cost | −£5 |
| Gross value after these costs | £90 |
This is still not take-home pay: tax and other deductions are personal. It is simply a cleaner view of the gross reward after the extra costs you entered.
3. Count the whole time commitment
If six paid overtime hours require 45 minutes of travel each way, the commitment is 7.5 hours rather than six. Comparing the amount left after costs with total committed time can reveal why two overtime opportunities with the same multiplier feel very different.
Comparison value per committed hour = value after incremental costs ÷ total committed hoursRun a frequency check before annualising
A single attractive overtime shift does not automatically translate into a reliable annual amount. If the six-hour example occurs twice a month, 24 occurrences produce £3,240 gross overtime pay before personal deductions and before the extra costs of working those shifts. If it occurs every week for 46 weeks, the same shift pattern produces £6,210 gross. Use a frequency that reflects what is realistically available, not the maximum your employer has occasionally offered.
When comparing overtime with a permanent salary change, keep the uncertainty visible. Contracted salary is normally more predictable than voluntary overtime, while compulsory or guaranteed arrangements may have different terms. The calculator annualises the frequency you enter; it does not predict how many shifts an employer will actually offer.
Contract and legal context comes first
GOV.UK notes that employers do not automatically have to pay overtime and that contracts usually set out any overtime rate. Working-time and minimum-wage rules are separate questions. Work Decisions does not determine whether an overtime arrangement is lawful or contractually required.