Using the rate calculator
Paid hours. Count the hours you are paid for. A 9:00 to 18:00 shift with an unpaid half-hour lunch is 8.5 paid hours, so at £30 an hour it is worth £255, not £270. Agree before the day whether the break is paid.
Weeks a year. A locum is not paid for holidays, bank holidays, sick days or the days spent on training. Taking 5.6 weeks off (the same as an employee's statutory holiday) leaves about 46 working weeks. Allow for quiet spells too, if you do not have shifts booked far ahead.
Expenses. The take-home figures assume the expenses you enter stay the same whatever your rate, which is usually close to true: your GPhC fee and indemnity do not go up because you charge more.
Why a few pounds an hour matters
At 8 hours a day, 4 days a week for 46 weeks, each extra £1 an hour is £1,472 a year before tax. Taking £5 an hour more is £7,360. Some of that goes in tax and National Insurance, which the take-home column allows for, but most of it stays with you.
For what other locums are being paid, and how to ask for more, read locum pharmacist rates and how to negotiate your rate.