SMP Calculator: How to Work Out Statutory Maternity Pay
Statutory Maternity Pay runs for up to 39 weeks at 90% of average weekly earnings for the first 6 weeks, then the lower of £194.32 or 90% of earnings for the remaining 33 weeks in the 2026-27 tax year [3]. Every figure an SMP calculator produces rests on one input, average weekly earnings, measured over an 8-week relevant period [1].
A calculator hides that arithmetic, but an employer still needs to know what it is doing, because the same numbers drive the employee's pay and the amount HMRC refunds. The official maternity, adoption and paternity calculator for employers works out leave dates, the relevant period and average weekly earnings from the due date and salary details [2].
This article explains what an SMP calculation needs, how average weekly earnings are worked out for weekly and monthly paid staff, how the two rates apply, and how part weeks are handled, ending with a full worked example.
Key takeaways
- An SMP calculation needs the due date, the qualifying week, the relevant period and the employee's gross earnings in that period.
- Average weekly earnings drive everything: 90% for 6 weeks, then the lower of £194.32 or 90% for 33 weeks.
- For monthly paid staff, average weekly earnings are found by dividing the relevant-period pay by the number of months, multiplying by 12 and dividing by 52.
- There is no daily rate of SMP, so part weeks are worked out as sevenths of the weekly rate.
- The employer recovers 92% of the SMP paid, or 109% under Small Employers' Relief, through the Employer Payment Summary.
What an SMP calculation needs
Before any pound figure is produced, a calculator establishes the dates that frame the whole entitlement and confirms the employee qualifies at all. Getting the dates wrong shifts the relevant period and changes the average.
The due date and the qualifying week
The starting input is the baby's due date, taken from the employee's MATB1 certificate, which a midwife or doctor issues from around 20 weeks before the birth [5]. From the due date, the calculator derives the qualifying week, which is the 15th week before the week the baby is due [1].
The qualifying week anchors both eligibility and the earnings window, so an error here cascades through the whole result [9]. The official employer calculator asks only for the due date and the pay details and derives these dates automatically, which removes the most common manual mistake [2]. An HMRC-recognised payroll software for SMEs performs the same derivation inside the payroll run.
Eligibility gates before any figure
A calculator should confirm eligibility before producing a number, because an employee who fails a gate gets nothing under SMP. The employee must have worked continuously for the same employer for at least 26 weeks running into the qualifying week, and must earn on average at least the Lower Earnings Limit of £129 a week [5]. They must also give the correct notice and proof of pregnancy [13].
If the employer decides the employee does not qualify, they must issue form SMP1 within 7 days of the decision and explain why, so the employee can claim Maternity Allowance instead [6]. The eligibility checker on GOV.UK lets an employee test entitlement to maternity pay, paternity pay or Maternity Allowance from their employment dates and earnings [10].
Calculating average weekly earnings
Average weekly earnings are the engine of the calculation. The method differs by how often the employee is paid, but the principle is the same: total the gross pay in the relevant period, then convert it to a weekly figure.
Weekly or irregular pay
For SMP, pay means gross pay due before deductions, including anything subject to National Insurance such as overtime, bonuses, arrears and holiday pay actually received in the relevant period [1]. The relevant period is normally the 8 weeks ending with the last payday on or before the Saturday of the qualifying week [9].
For a weekly paid employee, the calculator adds the earnings across that 8-week window and divides by 8 to get the average [1]. Because the window can catch a one-off payment, the average can sit above or below basic pay, which is exactly why the figure is calculated rather than assumed [3].
Monthly pay
For a monthly paid employee, the relevant period is usually the 2 monthly paydays falling in the window. The calculator adds the pay from those 2 months, divides by 2 to get a monthly average, multiplies by 12 to annualise it, then divides by 52 to get the weekly figure [1].
The table below sets out the two methods side by side.
| Pay frequency | Relevant period | Average weekly earnings formula |
|---|---|---|
| Weekly | The 8 weeks to the qualifying week | Total pay in the period divided by 8 [[1]](https://www.gov.uk/guidance/statutory-maternity-pay-manually-calculate-your-employees-payments) |
| Monthly | The 2 monthly paydays in the window | Total pay, divided by 2, multiplied by 12, divided by 52 [[9]](https://www.gov.uk/hmrc-internal-manuals/statutory-payments-manual/spm171100) |
The figure is not rounded to whole pence at this stage, because rounding early distorts the result that flows into the rate test [1].
Applying the two SMP rates
Once average weekly earnings are known, the rate structure is mechanical. The calculator applies a higher earnings-linked rate first, then a capped flat rate.
The 39-week structure
SMP is paid across a maximum of 39 weeks in two phases, with leave continuing unpaid afterwards. The first 6 weeks are paid at 90% of average weekly earnings with no cap, and the next 33 weeks at the lower of the flat rate or 90% of earnings [3]. The flat rate for the 2026-27 tax year is £194.32 a week [4].
| Period | Rate applied | Cap |
|---|---|---|
| Weeks 1 to 6 | 90% of average weekly earnings | None [[3]](https://www.gov.uk/maternity-pay-leave/pay) |
| Weeks 7 to 39 | Lower of £194.32 or 90% of earnings | £194.32 [[4]](https://www.gov.uk/guidance/rates-and-thresholds-for-employers-2026-to-2027) |
| Weeks 40 to 52 | Nothing, leave may continue unpaid | n/a [[13]](https://www.gov.uk/maternity-pay-leave/eligibility) |
Part weeks and rounding
SMP is a weekly payment, and there is no daily rate, so a calculator handles part weeks as fractions of a seventh [1]. A part week is worked out by dividing the weekly rate by 7, truncating to five decimal places, multiplying by the number of days due, then rounding up any part pence [1].
This matters most for monthly payrolls, where a maternity period rarely lines up neatly with calendar months, so employers pay part weeks at each end of a pay period [1]. Employers must keep SMP records for 3 years from the end of the relevant tax year, whether on form SMP2 or their own system [11]. A developer embedding this logic can call an HMRC-recognised payroll API so the seventh-based rounding is handled to the specification.
A full worked example
Consider a monthly paid employee whose relevant period covers 2 paydays of £3,200 each, a total of £6,400. The calculator divides £6,400 by 2 to get £3,200, multiplies by 12 to reach £38,400, then divides by 52, giving average weekly earnings of £738.46 [1].
Because £738.46 is above the £129 Lower Earnings Limit, the employee qualifies [5]. The first 6 weeks pay 90% of £738.46, which is £664.62 a week. From week 7, 90% of earnings (£664.62) is higher than the flat rate, so the £194.32 cap applies [4].
| Phase | Weekly amount | Weeks | Subtotal |
|---|---|---|---|
| Weeks 1 to 6 | £664.62 | 6 | £3,987.72 |
| Weeks 7 to 39 | £194.32 | 33 | £6,412.56 |
| Total | 39 | £10,400.28 |
The gross SMP comes to £10,400.28 over 39 weeks. PAYE income tax and Class 1 National Insurance are then deducted, because SMP counts as earnings [6]. An occasional employer paying a single member of staff can produce the resulting payslip with an instant payslip generator.
What the calculation feeds
The SMP figure is not the end of the process. It flows into the payroll submission and into the employer's reclaim, which together decide the real cost.
Reporting and reclaiming
SMP is reported as part of gross pay in the Full Payment Submission under Real Time Information, the regime that requires payroll software to be HMRC Recognised [12]. The employer then recovers most of the cost: 92% as standard, or 109% under Small Employers' Relief where Class 1 National Insurance was £45,000 or less in the previous tax year [7].
The reclaim is made through the Employer Payment Summary, and where deductions are too small to cover the SMP due, the employer can apply to HMRC for advance funding [8]. On the £10,400.28 above, a small employer recovers £11,336.31, leaving a surplus rather than a cost. Accountants tracking this across many clients use a multi-client payroll dashboard, and the totals can be cross-checked against the how much maternity pay is worth overview.
Conclusion
An SMP calculator is only as good as the inputs behind it: the due date, the qualifying week, the relevant period and the gross earnings in that period. From those, the arithmetic is fixed, 90% for 6 weeks, then a capped £194.32 for 33 weeks, with part weeks split into sevenths.
The same figures the calculator produces also set what the employer reports and reclaims, so an accurate calculation protects both the employee's pay and the employer's cash position. As statutory family pay grows more complex, the dependable route is a payroll system that calculates the entitlement and the recovery on the same run.
Frequently asked questions
How is statutory maternity pay calculated?
The calculation starts with average weekly earnings over the relevant period, normally the 8 weeks ending with the last payday before the qualifying week [1]. SMP is then 90% of those earnings for the first 6 weeks, followed by the lower of £194.32 or 90% of earnings for up to 33 more weeks [3]. The flat rate for the 2026-27 tax year is £194.32 [4].
How are average weekly earnings worked out for a monthly paid employee?
For a monthly paid employee, the employer adds the pay from the 2 paydays in the relevant period, divides by 2, multiplies by 12, then divides by 52 to reach the weekly average [1]. The figure should not be rounded to whole pence before the rate test is applied [9].
Is there a daily rate of statutory maternity pay?
No. SMP has no daily rate, so part weeks are worked out as fractions of a seventh of the weekly rate [1]. The weekly rate is divided by 7, truncated to five decimal places, multiplied by the number of days due, then any part pence is rounded up. This usually arises on monthly payrolls where the maternity period does not align with calendar months [1].
What does an employer need to use an SMP calculator?
The core inputs are the baby's due date from the MATB1 certificate, the employee's gross earnings in the relevant period and confirmation of at least 26 weeks of continuous service [5]. The official maternity, adoption and paternity calculator for employers derives the qualifying week, leave dates and average weekly earnings from the due date and pay details [2].
Image prompt: Documentary still life, a printed payroll worksheet and a desk calculator on an oak office desk, a maternity certificate and a pen beside them, a wall calendar softly out of focus in the background, natural daylight from a north-facing window, late morning, palette of warm white, paper cream, oak and brushed aluminium, the calculator and worksheet anchoring the lower-right two-thirds of the frame, shot on a Hasselblad X2D at 55mm f/4, photojournalism, soft film grain, no AI artefacts, no warped text, landscape orientation 16:9.
