How do you calculate days in accounts payable

You're finalising the board pack when the numbers stop agreeing. The days in accounts payable figure in your management accounts doesn't match the one in last week's lender covenant pack. Both started from the same creditor balance, but one was divided by cost of sales and the other by credit purchases.

Neither calculation is necessarily wrong. They use different methods, which can produce different versions of days payable outstanding (DPO). This guide explains the formula, how to choose the right inputs and how to interpret the result. It also includes a worked example in GBP and shows how DPO relates to the accounts payable turnover ratio.

Key takeaways

• Calculate DPO by dividing average trade payables by purchases or COGS, then multiplying by the number of days in the period.

• Use credit purchases when they best reflect the purchases that created the payable balance, or use COGS when that is the available or consistently reported denominator.

• Choose a clear VAT methodology and apply it consistently. Do not mix gross and net figures without explaining the effect.

• Compare DPO with supplier terms and actual payment data, but do not treat it as a precise measure of invoice lateness.

• Use the accounts payable turnover ratio as the inverse view of DPO. Dividing the number of days in the period by the turnover ratio should return the same result.

• Monitor invoice capture, approval, matching and payment stages to find the cause of rising DPO.

• Keep up to date with UK late-payment legislation, including the Commercial Payments Bill, because proposed rules are not the same as rules currently in force.

What days in accounts payable actually measure

Days in accounts payable is an estimate of how long a business takes to pay its trade suppliers. You'll also see it called DPO or accounts payable days. In UK accounts, it is often called creditor days.

The ratio compares a balance-sheet liability, trade payables, with a profit and loss flow such as purchases or cost of goods sold (COGS).

DPO is one component of the cash conversion cycle (CCC), alongside days inventory outstanding (DIO) and days sales outstanding (DSO). The Corporate Finance Institute's cash conversion cycle formula is:

CCC = DIO + DSO − DPO

A higher DPO reduces the cash conversion cycle and can leave cash in the business for longer. However, a rising DPO is not automatically good news. It may reflect better payment-term management, but it may also indicate invoices stuck in approval or suppliers being paid late.

Picture an AP manager telling the Finance Director that this month's increase came from invoices awaiting approval, while two key suppliers are already chasing payment. As Corporate Finance Institute explains, a high DPO can affect supplier relationships and may lead to tighter credit terms or restrictions.

How do you calculate days in accounts payable?

Divide average trade payables by purchases or COGS for the period, then multiply by the number of days in that period.

DPO = (Average trade payables ÷ Purchases or COGS) × Number of days in the period

Use 365 days for a full year. Use the actual number of days for shorter periods, such as 90 or 91 days for a quarter and 28, 29, 30 or 31 days for a month.

The formula is simple. Choosing and applying the inputs consistently is more difficult. Most DPO disagreements come from differences in the payable balance, the denominator, the VAT treatment or the day count.

At month-end close, a management accountant might pull the aged creditors report from Xero or Sage and use the total trade payables figure. That total may need adjusting before it is used in the calculation.

Choosing the accounts payable balance

Use the average trade payable balance for the period:

Average trade payables = (Opening balance + Closing balance) ÷ 2

Using only the closing balance can distort the result. For example, a large payment run on the last working day of the period may make the closing balance unusually low.

Include trade payables arising from ordinary supplier purchases. Usually, you should exclude balances such as:

• Accruals that do not relate to supplier invoices

• PAYE liabilities

• VAT liabilities owed directly to HMRC

• Corporation tax

• Capital creditors, if you are measuring operating supplier payments

The precise scope should match the denominator. If your denominator includes a particular category of supplier spend, make sure the payable balance reflects the related liabilities.

How should you treat VAT?

There is no single universal VAT treatment for every DPO calculation. The important rule is to avoid mixing incompatible bases.

UK purchase ledger balances often include VAT because they represent the gross amount owed to suppliers. Purchases and COGS, however, are usually reported net of recoverable VAT.

You can calculate DPO using a net or gross methodology, but document the approach and apply it consistently. If you remove VAT from the payable balance, make sure the denominator is calculated on a comparable basis. If you use reported gross trade payables, explain that choice and use the same methodology in every period.

The most important points are consistency, transparency and comparability between periods.

COGS or credit purchases?

Credit purchases can be a useful denominator because payables are created by purchases rather than by sales. AccountingTools explains that using COGS can produce a different payable-days figure because COGS reflects the cost of goods sold, not necessarily all purchases made on credit during the period.

COGS remains a common denominator, particularly when a business is using published accounts where detailed credit-purchase data is unavailable. It can also provide a useful comparison with other businesses if they use the same method.

A practical approach is:

• Use credit purchases where reliable figures are available and you want to measure supplier obligations against the purchases that created them.

• Use COGS when credit purchases are unavailable or when you need to follow a standard published-accounts methodology.

• Use total credit purchases of goods and services where that better reflects the supplier base, particularly in service businesses.

• Keep the same denominator from one reporting period to the next, or clearly explain any change.

There is no single denominator that is right for every business. The best method is the one that reflects the question you are trying to answer and can be applied consistently.

A worked example for a UK business

A UK wholesaler's financial controller needs one year-end DPO figure for the board pack and lender pack. The business has chosen a credit-purchases methodology, and all figures below are net of VAT.

Step 1: Calculate average trade payables

(£180,000 opening balance + £220,000 closing balance) ÷ 2 = £200,000

Step 2: Divide by annual credit purchases

£200,000 ÷ £1,460,000 = 0.137

Step 3: Multiply by the number of days in the year

0.137 × 365 = 50 days

Using COGS instead produces a different result:

(£200,000 ÷ £1,825,000) × 365 = 40 days

The 10-day difference comes from the denominator. Both figures may be useful, provided the business labels the methodology clearly and does not compare one method with the other as if they were identical.

Under the credit-purchases methodology, the reported DPO is 50 days. Compared with standard supplier terms of 30 days, that difference would warrant investigation. It does not, by itself, prove that every invoice is being paid 20 days late, because DPO is a balance-sheet ratio affected by purchasing patterns, timing and the composition of the payable balance.

To understand actual payment performance, compare DPO with invoice-level payment data, such as the time from invoice receipt or due date to settlement.

What is the best way to calculate the accounts payable turnover ratio?

The accounts payable turnover ratio measures how often a business clears its average trade payable balance during a period.

AP turnover ratio = Purchases or COGS ÷ Average trade payables

Use the same denominator and payable balance as in your DPO calculation.

For the wholesaler:

£1,460,000 ÷ £200,000 = 7.3

The business turned over its average trade payable balance 7.3 times during the year.

The two metrics are mirror images:

DPO = Number of days in the period ÷ AP turnover ratio

So:

365 ÷ 7.3 = 50 days

The figures reconcile because both calculations use credit purchases and average trade payables. If the turnover ratio uses COGS while DPO uses credit purchases, the two metrics will not reconcile.

Reading your DPO against supplier terms

DPO is most useful when viewed alongside supplier terms, payment performance and business context.

Compare it with contractual terms weighted by supplier spend, but treat the comparison as an indicator rather than a precise measure of lateness. DPO can be affected by the timing of purchases, seasonality, invoice receipt, payment runs and the balance of different supplier categories.

If DPO is materially above agreed terms, investigate whether the difference is caused by:

• Delays between invoice receipt and approval

• Purchase order or goods-received-note mismatches

• Payment runs that do not align with due dates

• Disputed invoices

• Seasonal purchasing patterns

• Incomplete or inconsistent payable data

If DPO is well below terms, the business may be paying early. That could be deliberate, particularly where early-payment discounts are attractive, but it may also mean the business is giving up working capital unnecessarily.

Early-payment discounts

An early-payment discount can justify a lower DPO when the financial benefit is greater than the cost of using the cash.

On 2/10 net 30 terms, paying on day 10 rather than day 30 earns a 2% discount for giving up 20 days of cash. A simple annualised calculation is:

(2 ÷ 98) × (365 ÷ 20) = approximately 37%

The discount may therefore be attractive unless the cash could earn or save more elsewhere. The exact decision should also consider tax, funding costs, cash availability and the supplier relationship.

Watch the DPO trend across several months rather than reacting to a single figure. A quarter-end payment freeze can lift DPO temporarily, but the operational impact may last longer if suppliers place the account on stop or delay further orders.

UK payment terms and the Commercial Payments Bill

Current GOV.UK guidance says that where a payment date is agreed, it must usually be within 30 days for public authorities or 60 days for business transactions. Businesses can currently agree a longer period than 60 days, but it must be fair to both parties. See the GOV.UK guidance on late commercial payments.

The Government introduced the Commercial Payments Bill to Parliament in May 2026. The Bill proposes maximum payment terms of 60 days for business-to-business payments, with strictly limited exemptions. It also proposes mandatory interest on late payments at 8% above the Bank of England base rate and additional powers for the Small Business Commissioner.

As of publication, the Bill is not yet in force and there is no confirmed commencement date. The Government has said that businesses will receive lead-in time and that the measures will not apply retrospectively. Finance teams should therefore monitor the legislation rather than treating the proposed rules as current law.

A DPO target based on payment terms longer than 60 days may need reviewing, particularly where a large business is paying smaller suppliers. However, the final scope, exemptions and implementation timetable should be checked against the latest official guidance before changing policies or contracts.

Late payment can also carry a direct cost. GOV.UK guidance on charging interest explains how statutory interest and debt-recovery costs may apply to eligible business-to-business debts.

Why there is no single good DPO

A good DPO depends on your agreed terms, sector, purchasing model, payment performance and supplier strategy.

For a public reference point, GOV.UK's large businesses' payment practices statistics report a median time to pay of 32 days for large businesses in 2025. The same commentary notes that the voluntary Fair Payment Code uses a benchmark of paying suppliers within 30 days.

For a closer comparison, the Check when businesses pay invoices service allows users to view published payment-practice reports.

Treat the comparison with care. The Government's payment-practice reporting measures the time between receipt of an invoice and payment. DPO is a balance-sheet ratio based on a payable balance and a purchases or COGS flow. The two figures can therefore diverge for the same business.

Use external benchmarks to provide context, not as a standalone target. Compare your own trend, actual payment performance and supplier terms before deciding whether your DPO is appropriate.

Common mistakes when calculating days in accounts payable

Most DPO errors come from the inputs and methodology:

• Mixing COGS and credit purchases between reports

• Switching between gross and net VAT treatment without documenting the change

• Using only the closing payable balance

• Including accruals, PAYE, VAT liabilities or capital creditors without matching them to the denominator

• Using the wrong number of days, such as 30 for a 31-day month

• Changing the methodology between periods, which makes the trend difficult to interpret

• Treating DPO as an exact measure of invoice payment lateness

• Comparing your DPO directly with another business that uses a different formula

Before reporting a figure, record the payable balance, denominator, VAT treatment, day count and period covered.

Improving AP performance without damaging supplier relationships

A DPO above agreed terms may trace back to process delays. Fix the process before renegotiating payment terms.

For example, an invoice might arrive on time but sit in a budget holder's inbox for three weeks. The supplier sees a late payer, while finance is blamed for a delay that happened earlier in the process.

If DPO rises while supplier terms remain unchanged, split the process into two stages:

1. Invoice received to approved

2. Approved to paid

Long approval times, purchase order mismatches or a growing exception queue can show where the additional days are coming from.

Practical improvements include:

• Capture invoices as soon as they arrive, rather than leaving them in personal inboxes.

• Route approvals to the right budget holder automatically.

• Use three-way matching to compare the invoice, purchase order and goods-received note.

• Schedule payments for the due date instead of relying on ad hoc payment runs.

• Keep supplier bank details and payment terms accurate.

• Agree longer terms with suppliers openly rather than stretching them unilaterally.

• Monitor invoice receipt, approval and payment dates separately.

With Spendesk's accounts payable automation, invoices can be routed to the right person through approval workflows. The platform supports matching invoices against purchase orders and delivery notes, mobile approvals and supplier payments from within the AP workflow.

Frequently asked questions

Are days in accounts payable and DPO the same thing?

Yes. Days in accounts payable, DPO and AP days generally refer to the same type of ratio. The calculation usually uses 365 days for a full year and the actual number of days for shorter periods.

Can you calculate DPO for a single month?

Yes, as long as you use that month's payable balance, purchases or COGS, and the actual number of days in the month. For example, March uses 31 days.

For a monthly figure, be aware that the opening and closing balances may be heavily affected by payment runs, seasonal purchases and invoice timing. It is often more useful to review the trend across several months.

Is a higher DPO always better?

No. A higher DPO may preserve cash, but it can also indicate delayed approvals, disputes or late payment. A DPO of 50 days compared with 30-day supplier terms is a reason to investigate, but it does not prove that all invoices are being paid 20 days late.

Should VAT be included in the accounts payable balance?

There is no universal answer. The key is to use a consistent and clearly documented methodology.

UK supplier balances often include VAT, while purchases and COGS are usually reported net of recoverable VAT. If you remove VAT from the payable balance, make sure the denominator is calculated on a comparable basis. Do not mix gross payables with net purchases without explaining the effect.

How do you calculate accounts payable for the DPO formula?

Start with the opening and closing trade payable balances and calculate the average:

(Opening trade payables + Closing trade payables) ÷ 2

For example:

(£180,000 + £220,000) ÷ 2 = £200,000

Then divide the average balance by purchases or COGS and multiply by the number of days in the period. Make sure you have defined which liabilities are included, how VAT is treated and whether the denominator is credit purchases or COGS.