To work out a pay in 3 payment, divide the total by three: a £150 order becomes three payments of £50. For pay in 4, divide by four (£37.50). Enter your price in the calculator above to see the split for 3, 4, 6 or 12 payments, then read on for how the maths changes with interest, vouchers and rounding.
This page is for information only. It is not financial advice or a recommendation to borrow, and the figures are examples rather than offers from any provider.
Pay in 3 vs pay in 4: the quick maths
With no interest and no fees, every instalment is simply the price divided by the number of payments. Here is the same £150 order split different ways:
| Payments | Each payment | Total repaid |
|---|---|---|
| 3 | £50.00 | £150.00 |
| 4 | £37.50 | £150.00 |
| 6 | £25.00 | £150.00 |
| 12 | £12.50 | £150.00 |
More payments make each one smaller, but you stay in the plan for longer. The total only stays the same if the plan really is interest-free and you pay on time.
When the price does not divide evenly
A £100 order split three ways is £33.33 a payment, which adds up to £99.99. Providers usually adjust one instalment by a penny (for example £33.33, £33.33 and £33.34), so the total still matches the price.
How the timing usually works
Many pay in 3 plans take the first payment at checkout, then the rest at set intervals, often monthly. Others split payments over weeks. Because the first instalment is paid straight away, a three-payment plan usually runs for about two months, not three.
Always check the payment dates shown at checkout. They decide when money leaves your account, which matters if your pay date falls between instalments.
What if there is interest? A worked example
Short interest-free splits are common, but longer plans can charge interest. For those, the calculator uses the standard loan method: the yearly rate divided by 12 gives a monthly rate, and the payment is worked out so the balance reaches zero at the end.
As an illustration only, take a £600 purchase over 6 months at a 20% APR:
- Monthly payment: about £105.91
- Total repaid: about £635.46
- Cost of spreading the payments: about £35.46
The same £600 over 6 interest-free payments would be £100 a month and cost nothing extra. Comparing the total repaid with the price is the clearest way to see what a plan really costs.
Take off the voucher first
Apply any discount before you split the bill, because the instalments are based on the final price. Suppose a £240 basket has a 10% code:
- Discounted total: £216.00
- Pay in 3: £72.00 each
- Pay in 4: £54.00 each
- 6 payments: £36.00 each
Use the Discount Calculator to get the reduced price, or the Stacked Discount Calculator if a sale and a code apply together. If delivery pushes the total up, the Free Delivery Calculator shows whether adding an item is worth it. Check the retailer allows codes with your chosen payment method, and look for current codes on PrimeVoucher's store pages.
UK rules: buy now pay later is now regulated
The Financial Conduct Authority (FCA) says it started regulating deferred payment credit, commonly called buy now pay later, on 15 July 2026. Lenders must now be authorised (or hold a temporary permission) and follow FCA rules. The FCA has said this includes proportionate affordability checks, clear information on payment dates and what happens if you miss one, access to the Financial Ombudsman Service, and support for customers in financial difficulty.
The FCA also says agreements made before that date remain exempt. Because details can differ between providers and plan types, check the current terms of the provider you are using. Source: FCA, Regulating Buy Now Pay Later (BNPL).
What to check before you choose a plan
- Total repaid: does it equal the price, or is there interest or a fee?
- Late payment consequences: find out what happens if a payment fails.
- Credit checks and reporting: providers differ in what checks they run and whether repayments are reported to credit reference agencies.
- Returns and refunds: check how a return affects instalments you have already paid or are still due.
- Your overall budget: several plans at once can add up to a large monthly commitment. Add them together before agreeing to another.
If repayments are worrying you, free, impartial guidance is available from MoneyHelper and from free debt advice charities.
Other ways to compare the cost
If you are weighing up paying in full against splitting the cost, include any cashback or discounts in the comparison. The Cashback & Voucher Calculator shows how these change the real price, and the Voucher Comparison Calculator helps you pick between a percentage and a pounds-off code.