How to Calculate (and Forecast) Accounts Payable

In this article we discuss:

• What Is Accounts Payable?

• Calculating the Accounts Payable Balance

• Understanding the Accounts Payable Turnover Ratio

• Accounts Payable Forecasting Formulas

• Best Practices for Building Your AP Forecast

• Powering AP Forecasting with Modern Tools

For finance teams, accounts payable (AP) is one of the most immediate indicators of cash commitments. It captures purchase activity and invoicing status while also signaling when liabilities are due. It sheds light on procurement cadence and supplier payment terms.

These insights are even more useful when used to look ahead. Forecasting future accounts payable based on historical patterns and current data helps finance teams anticipate obligations and integrate that outlook into broader liquidity strategy.

But today more than half of CFOs and finance leaders say outdated information hampers their ability to make accurate forecasts. An effective accounts payable forecast requires specific steps to build the right structure, logic, and technology tools into the AP process. When forecasting is built into regular planning, it gives finance leaders a dependable view of upcoming obligations and keeps teams aligned on spend, timing, and cash flow management.

What Is Accounts Payable?

Accounts payable represents the short-term liabilities your company owes to suppliers for goods and services already received. It appears on the balance sheet and reflects the timing, structure, and reliability of your payment practices.

Accounts payable also serves as a direct link between operational activity and cash flow. Each payable represents a known outflow, making AP one of the most visible signals of near-term liquidity needs. That’s why the first step to a reliable forecast is knowing exactly what’s owed and when.

Calculating the Accounts Payable Balance

Building a reliable AP forecast requires first knowing your current financial position. Knowing how to calculate your accounts payable balance is key, and can be done using a straightforward formula:

AP Balance = Total Purchases on Credit – Payments Made on Credit

This gives you a snapshot of what your company currently owes vendors for products or services received but not yet paid for. Most of this data lives in your general ledger and vendor subledgers. You can also find it on your balance sheet, listed under current liabilities.

Let’s say your company purchased $500,000 worth of goods on credit during the month. Over that same period, you paid $350,000 to vendors. Your ending accounts payable balance would be: $500,000 – $350,000 = $150,000

This figure reflects your outstanding obligations at a given point in time.

Accuracy here is non-negotiable. If your invoice tracking is delayed or payments aren’t properly recorded, you risk making flawed financial decisions. Timely and consistent data entry backed by integrated systems is key to maintaining a reliable balance and avoiding surprises in your cash flow statements.

When your accounts payable numbers are current and correct, you're better equipped to predict future payments, manage vendor relationships, and make confident decisions about capital allocation.

Understanding the Accounts Payable Turnover Ratio

Once your current AP balance is established, the next step is to assess how efficiently you’re managing those obligations. The accounts payable turnover ratio measures how often your business pays suppliers over a given period and reflects your payment behavior over time.

AP Turnover Ratio = Total Credit Purchases / Average Accounts Payable

A higher turnover ratio often indicates quicker payments, which can point to strong liquidity or short vendor terms. A lower ratio might suggest longer payment cycles or stretched cash flow, depending on the context.

This ratio also informs your days payable outstanding (DPO)—a metric that tells you the average number of days it takes to pay a supplier. While the turnover ratio shows frequency, DPO shows timing. Used together, they provide a fuller picture of your payment cadence and shape more accurate accounts payable forecasts.

Accounts Payable Forecasting Formulas

Now that you have a clear understanding of where your AP stands and how quickly payments are being made, the next logical step is to project what comes next. At this stage, forecasting formulas should help map expected payables based on known purchasing patterns, vendor agreements, and timing trends.

Two commonly used forecasting methods to generate projected accounts payable include:

• Forecasted AP = Forecasted Purchases × Historical AP %: This method works well for businesses with consistent procurement behavior and steady vendor terms. If your purchasing volumes don’t fluctuate dramatically and your payment patterns are predictable, this approach provides a straightforward way to extend current trends into the future.

Example: If you expect $500,000 in purchases next quarter and historically 30% of purchases remain unpaid at the end of a period, your forecasted AP would be: 500,000 × 0.30 = $150,000

• Forecasted AP = (DPO × COGS) / 365: This formula is a better fit for businesses with more variability in purchasing or seasonal shifts. It factors in Days Payable Outstanding and cost of goods sold to estimate how much is likely to remain outstanding based on your actual payment cadence.

Example: If your cost of goods sold is $1.2 million annually and your DPO is 45 days, your forecasted AP would be: (45 × 1,200,000) / 365 = $147,945.21

Choosing the right formula comes down to the rhythm of your purchasing and the flexibility of your vendor relationships. If activity is stable, the simpler method may give you exactly what you need. If things fluctuate, the DPO-based approach can offer a more dynamic view.

Either way, the value of the forecast depends on how consistently it’s updated and how well it reflects what’s really happening across procurement and payables.

Best Practices for Building Your AP Forecast

A strong forecast is shaped by the quality of your accounts payable process. Below are five actionable best practices to help you better manage cash flow and create forecasts that are more resilient, precise, and responsive to change.

1- Connect Data Across Functions

To build a complete forecast, integrate AP data with purchasing, procurement, and treasury systems. This helps you track your commitments before they become liabilities. For example, matching purchase orders to expected invoices can improve accuracy and reduce surprises.

2- Model Multiple Scenarios

Don’t rely on a single version of the future. Model different outcomes based on changes in vendor payment terms, price fluctuations, or procurement volume. Identify which vendors offer flexibility and which are high-risk, and run sensitivity analyses to understand how changes impact your cash position.

3- Create Rolling Forecasts With Defined Update Cycles

Shift away from one-and-done forecasts. Use rolling forecasts instead, and update monthly or alongside your close process. Establish a cadence to revise inputs such as COGS, payment behavior, and vendor additions to keep projections current.

4- Use Historical Trends to Build Predictive Logic

Analyze payment behavior over time. What are your average payment lags by vendor? When do discounts typically go unused? Use that data to establish patterns that inform more reliable forward-looking estimates and build in alerts when deviations occur.

5- Align Forecasts With Procurement and Business Cycles

Coordinate your forecast with known procurement cycles, product launches, or seasonal shifts in demand. For example, if Q4 typically sees a spike in raw material purchases, your forecast should reflect the timing and volume of those expected payables. Similarly, align payment projections with supplier delivery schedules or promotional calendars to mirror how purchasing activity maps to actual cash obligations.

6- Review Forecast Accuracy Post-Close

After each monthly or quarterly close, compare forecasted AP against actual outcomes. Identify where you over- or under-estimated obligations, and document the drivers of those variances. This regular feedback loop will help you refine your assumptions and continuously improve your forecasting model.

Powering AP Forecasting With Modern Tools

Manual forecasting methods fall short when finance teams need speed, accuracy, and adaptability. Modern financial management systems make it possible to forecast accounts payable with more precision and far less effort—especially when data, AP automation, and intelligence are built into the process from the start.

The majority of finance leaders (51%) reported to Workday that newer technologies—like financial management platforms that unify data from across the enterprise—are one of the most important elements for accelerating planning, execution, and analysis cycles. 

Platform-based tools provide the centralized data foundation teams need to execute the best practices we outlined above, improving finance decisions overall but also delivering critical benefits directly tied to accounts payable management, such as connecting data to business outcomes and executing faster cycles.

Capabilities to prioritize in a financial management software solution include:

• Automated invoice processing to streamline classification and validation

• Integration with purchasing systems to reflect real-time obligations

• AI and machine learning to identify outliers, predict payment behavior, and refine assumptions over time

• Connected actuals and commitments for a unified forecasting baseline

• Scenario planning and sensitivity analysis to test how changes in volume, timing, or cost affect outcomes

Modern forecasting tools do more than speed up calculations—they give finance teams the agility to act on changes in real time. When cash flow forecasts reflect current commitments and purchasing activity, teams can respond faster to shifting cash needs, adjust disbursement plans with confidence, and collaborate more effectively across finance and procurement.

Elevating Accounts Payable From Insight to Impact

Accounts payable is a powerful lens into a company’s financial rhythm. When calculated and forecasted with discipline and context, it enables sharper decisions, stronger supplier relationships, and tighter control of working capital.

In today’s environment, where liquidity visibility can make the difference between proactive growth and reactive belt-tightening, an accurate, agile AP forecast is more than helpful—it’s essential. And when accounts payable forecasting is embedded into regular financial planning, it stops being a one-off task and becomes a dependable source of insight.

39% of decision-makers are planning to invest more into payroll solutions over the next year. Learn how you can shift payroll from a back-office function to a strategic powerhouse in this Workday report.