Paying Early, Comparing Properly: The Rate Behind a Supplier Discount
An early-payment discount is rarely just a discount. It is a price for time. When a supplier offers terms such as 2% off if an invoice is settled 30 days before the normal due date, the finance team is effectively being asked to decide whether the firm can fund that earlier payment more cheaply than the discount is worth. For many UK SMEs, the answer changes once timing, VAT and working-capital strain are placed alongside the headline percentage.
Why a Percentage Needs a Clock
A 2% discount sounds modest. Compared with a 30-day acceleration, however, it can represent an annualised return well above the cost of many conventional funding lines. The comparison is only meaningful when the discount is expressed in the same units as an overdraft rate, an invoice finance facility or the firm’s own internal cost of cash.
The clock matters as much as the percentage. A supplier may describe terms as 2% for payment within 10 days, against a standard 30-day due date. In that case the acceleration is 20 days, not 30. If the standard due date is 60 days and the discounted date is 30, the acceleration is 30 days. Payment runs, weekends and bank holidays can shift the actual value dates, so the calculation should use the dates on which money would leave the firm’s account.
The Annualised Rate in One Line
The standard conversion is:
Annualised equivalent rate = [d / (1 - d)] x [365 / t]
Here, d is the discount expressed as a decimal and t is the number of days between the discounted payment date and the normal due date.
For a 2% discount in exchange for paying 30 days early:
- d = 0.02
- 1 - d = 0.98
- t = 30
- Annualised rate = (0.02 / 0.98) x (365 / 30) = approximately 24.8%
That is the rate the firm is effectively earning on the cash it pays early, or paying if it borrows to do so. A 2% discount over 20 days produces a higher annualised figure of approximately 37.2%. The shorter the acceleration, the more expensive the discount is in annualised terms.
This rate is not a recommendation. It is a common language for comparison.
A Worksheet for the Finance Team
The following worksheet can be completed for any supplier offer. The example uses a £10,000 net invoice with £2,000 VAT, standard terms of 60 days and a discounted payment date 30 days earlier. The figures should be replaced with the actual invoice and value dates.
| Item | Example | Your figures |
|---|---|---|
| Net invoice value | £10,000 | |
| VAT | £2,000 | |
| Gross invoice value | £12,000 | |
| Standard due date | Day 60 | |
| Discounted payment date | Day 30 | |
| Days paid early (t) | 30 | |
| Discount rate (d) | 2.0% | |
| Cash paid if discount taken | £11,760 | |
| Cash paid at standard terms | £12,000 | |
| Cash saved before VAT recovery | £240 | |
| Annualised discount rate | 24.8% | |
| Overdraft all-in annual rate | 9.0% | |
| Invoice finance all-in annual rate | 18.0% | |
| Firm’s opportunity cost of cash | 4.0% | |
| Change in days payable outstanding | -30 days | |
| Change in cash conversion cycle | +30 days |
The worksheet should be accompanied by a short narrative. Which funding source would actually be used? Is the overdraft available, or merely theoretical? Does the invoice finance facility carry a service fee, minimum charge or concentration limit that raises the all-in cost? Would paying early breach a covenant or leave insufficient headroom for payroll and tax?
VAT Is a Timing Item, Not a Discount
For a VAT-registered UK SME, the VAT element of an invoice is usually recoverable, subject to the normal rules. A discount may reduce the VAT charged if the supplier applies it correctly, but the finance team should separate the permanent economic saving from the cash-flow movement.
In the example, the cash saving before VAT recovery is £240. If the firm recovers VAT, the enduring saving is closer to the net discount, while the VAT portion is largely a timing matter between payment, recovery and the VAT return. Annualising the gross cash movement without noting the recovery position can overstate the benefit. It can also understate the working-capital gap if VAT recovery is slow or the firm is partially exempt.
The invoice should be checked for whether the discount applies to the net amount, the gross amount or a specified element such as freight. The payment run should be checked for whether the discounted amount is what is actually remitted. A discount that is not correctly reflected in the VAT records creates unnecessary reconciliation work.
The Cash Cycle Does Not Disappear
Paying 30 days early reduces days payable outstanding by 30 days. In a simple cash conversion cycle of inventory days plus receivable days minus payable days, that change lengthens the cycle by 30 days. The firm must fund that gap from somewhere: surplus cash, overdraft, invoice finance, a director’s loan or delayed payments elsewhere.
This is why a discount can be a poor decision even when its annualised rate looks high. If the only available funding is an overdraft at 9%, the arithmetic may favour the discount. If the firm would need to use a more expensive facility, eat into a tax reserve or strain supplier relationships by stretching other payables, the apparent gain may be illusory.
A useful test is to ask what happens in the month the discount is taken. Does the bank balance remain above the firm’s minimum operating buffer? Are payroll and VAT payments still covered? Would the firm need to delay a planned capital purchase or draw further on a facility? A discount is a borrowing decision even when no loan is drawn.
When the Discount Is Really a Price Adjustment
The finance team should also test whether the discount is genuine. If the supplier’s base price has been set with the discount in mind, taking the discount may simply return the firm to a market price. Comparing the discounted price with alternative suppliers, and with the same supplier’s terms for other customers or volumes, is more informative than comparing it with the supplier’s own standard price.
It is reasonable to ask whether the standard terms can be extended instead. A supplier that offers 2% for 30 days early may be more valuable as a supplier that offers 60-day terms without discount. The firm should compare total cost, not just unit price: payment terms, delivery reliability, minimum order quantities and the administrative cost of more frequent payment runs all form part of the commercial package.
A Four-Line Decision Note
Before accepting an early-payment discount, the finance team should record four lines: the annualised rate of the discount, the all-in annual cost of the funding that would be used, the effect on the cash conversion cycle, and the post-payment cash buffer. If the discount rate is clearly above the funding cost and the buffer remains intact, the offer merits serious consideration. If the rate is close, or the funding source is uncertain, the safer course is usually to keep the cash and preserve flexibility.
The discount is not free. It is a trade of cash today for a saving later. In 2026, with tighter margins and higher scrutiny on working capital, UK SMEs should make that trade with the same discipline they apply to any other financing decision.
