Blog · Finance metrics and formulas · Professional services
Service companies can compare customer collection with supplier payment timing without inventing inventory. Build the calculation from receivables, payables and matched costs, then keep unbilled work and payroll visible.
The cash conversion cycle for service companies compares the time customers take to pay with the time the business takes to pay suppliers, usually without an inventory component. Start with consistent receivables and payables balances, then declare which costs support the payable-days denominator. Keep work waiting to be billed outside the invoice collection measure.
The cash conversion cycle formula combines inventory days, receivables days and payables days. For an inventory-free service business, inventory days drop out:
Inventory-free, cost-based cash cycle = Receivables days − Payables days
Receivables days = Average trade receivables / Credit revenue × Period days
Cost-based payables days = Average trade payables / Cost of services × Period days
The CFA Institute identifies receivables days and payable days as operating activity measures and the cash conversion cycle as a liquidity measure. It does not make this calculation a complete cash forecast.
Service costs may include salaries, while trade payables largely contain subcontractors and other vendors. For operational payment timing, calculate an additional measure using only purchases financed through those payables. Call it supplier-payment days and label the resulting collection-to-supplier gap explicitly. It answers a different question from the cost-based cycle.
Do not invent inventory to make a service company resemble a manufacturer. The IRS guide's discussion of businesses that sell services distinguishes services without income-producing merchandise from businesses that calculate merchandise cost of goods sold. That is tax guidance, rather than a financial-reporting classification rule, but it illustrates why a merchandise assumption can be inappropriate.
Use a receivables aging at the opening and closing dates, the credit-sales register, matching payables snapshots and a supplier invoice register. Add the service-cost ledger and an unbilled-work report. Retain customer, project, supplier, invoice date, due date, payment date, currency and business unit where available.
The example is an illustrative US consulting company for January 1 through March 31, 2026, a 90-day quarter. All revenue is credit revenue. Balances exclude tax, intercompany entries, loans and customer deposits.
| Input | Opening balance (USD) | Closing balance (USD) | Quarter activity (USD) |
|---|---|---|---|
| Trade receivables | 240,000 | 360,000 | — |
| Trade payables | 90,000 | 150,000 | — |
| Credit revenue | — | — | 900,000 |
| Supplier service purchases charged to service costs | — | — | 360,000 |
| Employee service costs | — | — | 270,000 |
| Total service costs | — | — | 630,000 |
Here every supplier purchase passes through trade payables. Employee costs do not. That scope is why a supplier-spend denominator and a total-service-cost denominator produce different payable days. The cost of goods sold guide explains the cost boundary more generally; this calculation uses the company's declared service-cost policy.
Enter the table above with its header in row 1 and opening, closing and activity amounts in columns B, C and D. Put period days, 90, in H1. The formulas below use those spreadsheet cells.
Average receivables: =AVERAGE(B2:C2)
Average payables: =AVERAGE(B3:C3)
Receivables days: =AVERAGE(B2:C2)/D4*$H$1
Cost-based payables days: =AVERAGE(B3:C3)/D7*$H$1
Supplier-payment days: =AVERAGE(B3:C3)/D5*$H$1
Cost-based cycle: =AVERAGE(B2:C2)/D4*$H$1-AVERAGE(B3:C3)/D7*$H$1
Supplier timing gap: =AVERAGE(B2:C2)/D4*$H$1-AVERAGE(B3:C3)/D5*$H$1
The text before each equals sign is a cell label, not part of the formula. Use unrounded values in subsequent calculations; displayed days are rounded to one decimal.
| Step | Calculation | Result (balances in USD; other rows in days) |
|---|---|---|
| Average receivables | (240,000 + 360,000) / 2 | 300,000 |
| Average payables | (90,000 + 150,000) / 2 | 120,000 |
| Receivables days | 300,000 / 900,000 × 90 | 30.0 |
| Cost-based payables days | 120,000 / 630,000 × 90 | 17.1 |
| Cost-based cycle | 30 − 17.142857 | 12.9 |
| Supplier-payment days | 120,000 / 360,000 × 90 | 30.0 |
| Collection-to-supplier gap | 30 − 30 | 0.0 |
The zero supplier gap does not mean the company needs no working capital. The employee service costs still require funding, and their actual payment dates are absent from that measure. Never compare the zero-day gap with another company's cost-based cash cycle as though their denominators matched.
Tie each aging snapshot to the corresponding trade-control account. Supplier purchases must reconcile to the selected vendor-cost rows, and 360,000 + 270,000 must equal the 630,000 service-cost total. Reverse the days calculations as a further check: 30 / 90 × 900,000 returns 300,000, and unrounded cost-based payable days / 90 × 630,000 returns 120,000.
Balance-based days sales outstanding is not the average invoice payment lag. Inspect settled invoices separately with =PaymentDate-InvoiceDate, and unpaid invoices against the report date. Otherwise, a late billing run can make collection look fast simply because completed work has not reached receivables.
Give unbilled work its own owner, amount and milestone date. Track completion-to-invoice days without adding the unbilled balance to receivables while leaving the denominator unchanged. Subscription advance billing needs a different interpretation, covered in cash conversion cycle for software companies.
Bring receivables and payables snapshots, a service-cost export and invoice dates to Covirage. Its tools compute and check the figures; the external AI model explains the results with every figure traced to its rows. Create a free Covirage account, set up your business and bring a sample of your own data.
See Covirage for professional services for the business context.
A business with no inventory has no inventory-days component. Some service businesses also sell materials or hold goods, so inspect the actual ledger rather than assuming zero. Unbilled hours should remain a separate billing measure unless their accounting classification requires otherwise.
A conventional cost-based DPO may use service costs that include payroll. A supplier-payment measure should instead match trade payables with the supplier purchases that create them. Disclose both definitions and review payroll timing separately because employee payments do not normally pass through trade payables.
No. Matching customer and supplier days says little about payroll paid before collection, taxes, advance supplier payments or unfinished work. Use the cycle alongside a dated cash schedule and an unbilled-work report before drawing a conclusion about funding.