Starting Mid-Year: Pro Rata for Part-Year Workers

Most salary discussions assume you work the full year. But what happens when you join in September, leave in March, or take an unpaid career break? Your pay for that first or last year needs pro rata salary starting mid year treatment — a second layer of pro-rating on top of any part-time fraction. Done correctly, you are paid fairly for exactly the portion of the year you worked. Done badly, you can lose hundreds of pounds.

Two kinds of pro-rating, and how they combine

It helps to separate the two calculations clearly:

1. Part-time pro-rating: FTE salary × (your hours ÷ full-time hours) — this gives your annual salary as if you worked the whole year.
2. Part-year pro-rating: annual salary × (portion of the year worked) — this adjusts for joining or leaving mid-year.

Worked example: You join on 1 October on a £30,000 FTE salary, working 22.5 hours of a 37.5-hour week.

• Part-time salary: £30,000 × (22.5 ÷ 37.5) = £30,000 × 0.6 = £18,000 per full year
• Tax year runs 6 April to 5 April; you work 1 October to 5 April = roughly 6 months
• Part-year pay: £18,000 × (6 ÷ 12) = £9,000 for the part-year

In practice, payroll rarely uses whole months — it counts days. More on that below.

How payroll counts the days

For part-year calculations, employers typically use one of two methods:

• Calendar days: (days employed ÷ 365) × annual salary. Simple and transparent.
• Working days: (working days employed ÷ 260) × annual salary. Used where pay is closely tied to days actually worked.

Worked example — calendar-day method: You start work on 16 September. From 16 September to 31 December is 107 days. Your part-time annual salary is £18,000.

£18,000 × (107 ÷ 365) = £18,000 × 0.2932 = £5,276.71 for the period.

Most monthly payrolls will then spread this across the remaining paydays of the year, or pay it as a proportion each month. Either way, the total for the part-year should equal the day-counted figure.

Table: part-year pay on an £18,000 pro-rata salary (calendar days)

Holiday entitlement for part-year workers

For a month-by-month answer, use our holiday entitlement calculator for mid-year starters.

Holiday is pro-rated twice for someone who is both part-time and part-year: once for hours, once for the portion of the year worked.

Worked example: Full-time entitlement is 28 days (5.6 weeks). You work 0.6 FTE and join on 1 October (3 months of the leave year remaining).

• Part-time entitlement: 28 × 0.6 = 16.8 days for a full year
• Part-year entitlement: 16.8 × (3 ÷ 12) = 4.2 days

Employers usually round up to 4.5 or 5 days rather than dealing in fractions of a day. If you leave part-way through the year, the same maths runs in reverse: holiday accrued = full entitlement × fraction of the year worked, and any untaken balance is paid in your final pay.

The tax wrinkle: emergency tax codes

Here is the part that surprises most mid-year starters. When you join without a P45, payroll often puts you on an emergency tax code (often 1257L on a “month 1” basis). This means:

• Your personal allowance is spread as if you started in April, which can over-tax you in the early months.
• Once HMRC issues your correct cumulative code, the overpaid tax is refunded through payroll automatically.

So if your first payslip’s take-home looks lower than expected, check whether the tax code is emergency (it will say something like “1257L M1” or “1257L W1”). The gross pay should still match your part-year calculation — it is the tax line, not the salary line, that is usually responsible. If you want to verify the gross figure independently, run your numbers through our free pro rata salary calculator and compare.

Leaving mid-year: final pay and holiday pay

When you resign or are made redundant part-way through the year, three calculations land in your final pay:

1. Salary to your leaving date, day-counted from your annual pro-rata salary.
2. Accrued but untaken holiday, paid at your daily rate: annual salary ÷ 260 × untaken days.
3. Any contractual bonuses or commissions, pro-rated to your leaving date if the scheme rules allow it.

Worked example: Your pro-rata salary is £21,000. You leave on 15 May, having taken 6 days of your 16.8-day part-time entitlement. The leave year started 1 January.

• Days worked: 1 Jan to 15 May = 135 days → £21,000 × (135 ÷ 365) = £7,767.12 salary
• Holiday accrued: 16.8 × (135 ÷ 365) = 6.21 days
• Untaken: 6.21 − 6 = 0.21 days → 0.21 × (£21,000 ÷ 260) = 0.21 × £80.77 = £16.96 holiday pay
• Final gross: £7,767.12 + £16.96 = £7,784.08 (plus any bonus due)

If you have taken more holiday than accrued, the employer can deduct the excess from final pay — but only if your contract allows it. Check before you book that long May holiday.

Unpaid leave and career breaks

Unpaid parental leave, sabbaticals and career breaks create part-year patterns too. The principles are the same:

• Salary stops (or reduces) for the unpaid period, calculated by days.
• Holiday continues to accrue during most statutory leave, including maternity and parental leave — it is not lost because you were not being paid.
• Pension contributions usually pause during unpaid leave unless you arrange voluntary contributions.
• Continuous service is generally preserved, which matters for redundancy and notice rights.

If you are planning a career break, ask payroll for a written illustration of how your pay and holiday will be handled. Surprises are much harder to fix retrospectively.

Fixed-term contracts and the part-year trap

Fixed-term employees sometimes discover their “annual salary” was quietly part-yeared without the maths being shown. If you are offered a 9-month contract at “£24,000 pro rata”, clarify whether that means:

• £24,000 is the FTE annual rate, and you will receive £24,000 × (9 ÷ 12) = £18,000, or
• £24,000 is what you will actually receive for the 9 months (implying a £32,000 FTE rate).

These are very different offers. Always ask: “Is that the full-year equivalent or the actual amount I will be paid?” Get the answer in writing before you sign.

Other date-based calculations: joining mid-month · leaving mid-month · partial month · start and end dates · days worked · daily rate · notice pay · redundancy pay

FAQs

How is pro rata salary calculated when starting mid-year?

First calculate your full-year pro-rata salary (FTE salary × your hours fraction), then multiply by the portion of the year you work — usually counted in days: annual salary × (days employed ÷ 365).

Does holiday entitlement reduce if I start mid-year?

Yes. Holiday is pro-rated for the portion of the leave year you work, on top of any part-time pro-rating. A 0.6 FTE starter joining with 3 months of the leave year left gets roughly a quarter of their part-time entitlement.

Why is my first payslip taxed so heavily when I start mid-year?

You are probably on an emergency tax code. Your personal allowance is being spread as though you worked the full year, which over-taxes the early months. HMRC will issue a correct cumulative code and payroll will refund the difference automatically.

If I leave mid-year, do I lose unclaimed holiday?

No — accrued but untaken holiday must be paid in your final pay at your daily rate. But check your contract: if you have taken more than you accrued, the excess can usually be deducted.

Start clear, finish fair

Mid-year starts, mid-year departures and career breaks all use the same honest principle: pay for exactly the time worked, counted in days, on top of a correctly calculated pro-rata salary. When employers show the maths and employees know how to check it, part-year pay is completely uncontroversial.

Before you sign that offer letter or hand in your notice, run the figures through the free pro rata salary calculator so you know exactly what the part-year should be worth.

Notice periods, PILON and part-year pay

If your employment ends with a notice period, how the notice is handled affects your part-year calculation. Two scenarios:

• You work your notice. Pay continues normally to your leaving date, day-counted as above. Straightforward.
• Payment in lieu of notice (PILON). The employer pays out your notice period as a lump sum instead of requiring you to work it. The lump sum is based on your normal pro-rata salary for the notice length — e.g. one month’s notice on a £18,000 pro-rata salary means a £1,500 PILON payment, taxed as earnings.

One subtlety: holiday continues to accrue during a worked notice period but not during a PILON period (since employment has ended). That can shift your final holiday-pay figure by a day or two, so it is worth checking the leaving date payroll actually used. If your P45 shows a leaving date earlier than you expected, query it — the date drives both the salary and holiday calculations.

The 12.07% shortcut for irregular part-year workers

For workers with irregular hours — casual, zero-hours or seasonal staff — many employers now calculate holiday accrual at 12.07% of hours worked (the statutory 5.6 weeks expressed as a percentage of working time). If you join mid-year on irregular hours, your holiday builds up as 12.07% of every hour you work, which automatically handles the part-year element with no separate calculation needed.

Worked example: You work 60 irregular hours between joining in October and December. Holiday accrued: 60 × 12.07% = 7.24 hours of paid leave. Simple, transparent, and it matches what the law expects for irregular-hours workers.

Related reading

• Pro Rata Salary Formula with Worked Examples
• 37.5 vs 40-Hour Week: Pro Rata Compared