What a Prorated Salary for Joining Mid-Month Means
When you join a new job part-way through a month, you are not paid for the whole month. You are paid only for the days from your start date to the end of that month, and that amount is called your prorated salary for joining mid-month. In the UK, employers usually work this out by dividing your monthly salary by the number of days in that month, or by the number of working days, and then multiplying by the number of days you actually worked. The exact method matters, because the two approaches can give different answers in the same month.
This guide explains both methods, shows worked examples for common start dates, and covers the details that catch new joiners out: how your first payslip is timed, what happens to holiday, pension and National Insurance in a part-month, and what to check before you query a figure. Use it alongside our free pro rata salary calculator to test your own numbers.
The Two Main Calculation Methods
Most UK employers use one of two methods for a mid-month start. The first is the calendar-day method. Your annual salary is divided by 12 to get a monthly salary, then divided by the number of calendar days in the month, then multiplied by the number of calendar days from your start date to the end of the month, inclusive. This method is simple and treats every day in the month equally, including weekends.
The second is the working-day method. Your monthly salary is divided by the number of working days in that month, usually Monday to Friday excluding bank holidays, then multiplied by the number of working days you actually worked. This method pays more per day in a month with fewer working days, and it matches how many payroll systems think about a working week. Some employers also use a fixed 260-working-day year, dividing the annual salary by 260 and multiplying by working days, which is a close cousin of this method.
Neither method is universally “correct”. What matters is what your contract and your employer’s payroll policy say. A contract that says salary is “payable monthly in arrears” with no further detail usually means the employer will apply its standard payroll practice, and you should ask payroll which method they use if your first payslip looks unexpected. The difference is rarely huge for a mid-month start, but it can be £50 to £150 on a typical salary, so it is worth understanding.
Worked Example: Joining on the 15th
Take an employee joining on a £30,000 annual salary on 15 April. The monthly salary is £30,000 divided by 12, which is £2,500. April has 30 calendar days. From 15 April to 30 April inclusive is 16 calendar days. Using the calendar-day method: £2,500 divided by 30, multiplied by 16, equals £1,333.33.
Using the working-day method, April 2026 has 22 working days, Monday to Friday, with no bank holiday in the period after the Easter weekend depending on the year. From 15 April to 30 April there are 12 working days. The calculation is £2,500 divided by 22, multiplied by 12, which equals £1,363.64. The working-day figure is slightly higher here, because the working days in the second half of April are a slightly larger share of the month’s working days than the calendar days are of the month’s calendar days.
Now take a different month. Joining on 15 February, a 28-day month, on the same £30,000 salary: the calendar-day calculation is £2,500 divided by 28, multiplied by 14, which equals £1,250. The working-day calculation, with 20 working days in February and 10 working days from the 15th onwards, is £2,500 divided by 20, multiplied by 10, which also equals £1,250. In this case the methods agree. The lesson is that the method matters most in months where weekends fall unevenly, and in 31-day months.
Worked Examples at Different Salaries
The table below uses the calendar-day method for a start on the 16th of a 30-day month, where 15 calendar days remain, exactly half the month. In that neat case, the prorated pay is simply half the monthly salary, which makes it a useful sanity check.
Annual salary £24,000: monthly £2,000, prorated for 15 of 30 days £1,000. Annual salary £30,000: monthly £2,500, prorated £1,250. Annual salary £36,000: monthly £3,000, prorated £1,500. Annual salary £45,000: monthly £3,750, prorated £1,875. Annual salary £60,000: monthly £5,000, prorated £2,500. If your start date is not exactly halfway through the month, scale the figure by the days you worked divided by the days in the month.
For a start on the 10th of a 31-day month, 22 calendar days remain. On £36,000, the monthly salary is £3,000, and the prorated pay is £3,000 divided by 31, multiplied by 22, which equals £2,129.03. For a start on the 20th of a 31-day month, 12 days remain, and the same salary gives £3,000 divided by 31, multiplied by 12, which equals £1,161.29. Always count your start date itself: if you start on the 20th, that day counts as a worked day, unless your contract says otherwise.
Part-Time Joiners: Combining Mid-Month and Pro Rata
If you join mid-month on a part-time contract, two prorations apply at once. First, your annual salary is already pro-rated for your working pattern, for example 0.6 FTE or three days a week. Second, that part-time monthly salary is prorated again for the part of the month you worked. The order does not matter, because multiplication is commutative, but both steps must be applied, or you will overstate your first pay.
For example, a full-time equivalent salary of £30,000 at 0.6 FTE gives a part-time annual salary of £18,000, or £1,500 a month. Joining on 15 April, with 16 of 30 calendar days worked, the first month’s pay is £1,500 divided by 30, multiplied by 16, which equals £800. A common mistake is to apply the mid-month fraction to the full-time salary and then forget the FTE fraction, which would double the figure to £1,333.33 and set up a disappointing correction later.
Shift workers and term-time staff need extra care. If your working pattern is not spread evenly across the month, a simple calendar-day split may not reflect the shifts you actually worked. In that case, payroll will often pay by the shifts or hours worked in the period, rather than by a day fraction. Ask for a breakdown if your first payslip does not match a day-based estimate, and check whether your contract defines a different method for irregular patterns.
Your First Payslip: Timing, Tax and National Insurance
Most UK employers pay monthly in arrears, which means work done in April is paid at the end of April or in early May, depending on the payroll cut-off. If you join after the payroll cut-off, your first payment may arrive a month later and cover two part-periods, or you may receive a separate payment for the stub period. Neither is an error by itself, but it can make the first payslip look surprisingly large or small.
Income tax in a part-month is usually calculated on a cumulative basis through PAYE, which spreads your tax-free personal allowance across the year. In your first month, you may be taxed on an emergency code if your P45 has not arrived, which can overstate the tax deduction. The overpayment is usually corrected automatically in later months once the correct code is applied, or through a tax refund at the year end. National Insurance, by contrast, is calculated per pay period, not cumulatively, so a part-month’s National Insurance is based on that period’s earnings alone, and a low first month may fall below the threshold and attract no National Insurance at all.
Pension contributions in a part-month follow the same pattern: they are usually a percentage of pensionable pay in that period, so a half-month’s pay gives a half-month’s contribution. Some schemes have a waiting period before auto-enrolment, so check whether pension deductions start immediately or after three months. Holiday entitlement also accrues from your start date, usually at one twelfth of the annual entitlement per month worked, so a mid-month start gives a small pro-rated holiday balance in the first month, not a full month’s worth.
Common Mistakes and What to Check
The most common mistake is counting the wrong number of days. Count inclusively from your start date to the last day of the month, and be clear about whether weekends are included. If your employer uses working days, count only Monday to Friday, excluding bank holidays that fall in your worked period. A second mistake is using the wrong monthly salary: if you are part-time, use your part-time monthly salary, not the full-time equivalent figure quoted in the job advert.
A third mistake is forgetting that a month’s pay may be split across two payslips if you join near the cut-off, or that overtime, allowances and deductions are added after the basic prorated figure. Always compare your payslip’s gross pay with your own calculation, and if the difference is more than a few pounds, ask payroll for the method and the day count they used. Payroll teams deal with this question every month, and a polite request for the breakdown usually resolves it quickly.
Finally, keep your own record. Note your start date, annual salary, FTE fraction, the method you believe applies, and the figure you expect. If a correction is needed, that record makes the conversation much shorter. It also helps when you come to check your P60 at the year end, because a part-year’s earnings will not match a full year’s salary, and that is expected, not an error.
Other date-based calculations: leaving mid-month · partial month · start and end dates · days worked · daily rate · starting mid-year · notice pay · redundancy pay
Frequently Asked Questions
Do I get paid for the days before I start? No. Prorated pay covers only the period from your start date. Days before you joined are not paid, and days after you leave are covered by the leaving calculation, not the joining one.
Does my employer have to use the calendar-day method? No. UK law does not prescribe one method for monthly-paid staff. The contract and the employer’s payroll policy decide, so check both, and ask payroll if the method is not stated.
What if I start on a weekend or a bank holiday? Your start date is still your start date for pay purposes, even if it is not a working day. The day count will depend on the method: calendar-day counts include it, working-day counts will start from the next working day, so the two methods can diverge slightly in that case.
Will my second month’s pay be a full month? Yes, in most cases. Once you have worked a full calendar month, you receive the full monthly salary, subject to any deductions, overtime or unpaid leave in that month.