How Overbilling and Underbilling Work
Contractors often bill customers according to contractual schedules, milestones, progress certificates, or approved applications for payment. Revenue recognition, however, follows the project's actual progress and the applicable accounting policy. Because billing dates and revenue recognition do not always coincide, a project may show an overbilled or underbilled balance at a reporting date.
A Billing System manages the creation and processing of customer charges, while a Billing Document records the details of a specific invoice or billing transaction. Reviewing these records alongside job costs and recognized revenue allows accounting teams to reconcile what has been billed with what has been earned.
For example, a contractor may receive an advance payment or invoice a customer for a scheduled milestone before completing the associated work. The project can be overbilled even when the cash has already been received. Conversely, a contractor may complete substantial work but have to wait for an approved progress certificate before invoicing, resulting in underbilling.
Calculating Overbilling and Underbilling
A common approach compares cumulative customer billings with cumulative earned revenue at a specific reporting date. Both figures should relate to the same project and period, and earned revenue should be determined using the company's applicable accounting method.
Overbilling or Underbilling Position = Cumulative Billings − Cumulative Earned Revenue
A positive result indicates overbilling, while a negative result indicates underbilling. A zero result means cumulative billings equal cumulative earned revenue.
Consider a construction project with $420,000 in cumulative customer billings and $350,000 in earned revenue at month-end.
Calculation: $420,000 − $350,000 = $70,000.
The project has a $70,000 overbilling position. This means the contractor has billed $70,000 more than the revenue earned to date. The balance may provide working capital for upcoming project expenses, but the team must still deliver the remaining contracted work and satisfy its obligations.
If the same project had $300,000 in billings and $350,000 in earned revenue, it would have $50,000 in underbilling. That amount may represent work performed but not yet billed, subject to contract terms and applicable accounting requirements.
Financial Impact on Cash Flow and Reporting
Overbilling and underbilling provide insight into the timing difference between project execution and customer invoicing. Overbilling can support near-term cash flow because billings may precede the related costs of completing work. However, the funds may be needed to meet future labor, material, subcontractor, and equipment expenses.
Underbilling can indicate that a contractor has financed work before billing the customer. Persistent underbilling may delay cash collection, increase working capital requirements, and place pressure on the project's ability to fund ongoing operations. Finance teams should investigate delayed approvals, unsubmitted invoices, missing change-order approvals, and differences between job-cost records and progress reports.
Neither position automatically means a project is profitable or unprofitable. Profitability depends on expected contract revenue and total project costs, while overbilling and underbilling measure the relationship between earned revenue and customer billings.
Monitoring Billing Accuracy in Sage 100
Effective monitoring requires current job-cost transactions, accurate customer invoices, documented project progress, and regular reconciliation. Finance teams should review each project's billing position at month-end and investigate significant changes from the previous reporting period.
Billing Verification supports the review of billing amounts against contract terms, approved change orders, completed work, and supporting documentation. Where invoice capture, extraction, validation, matching, and approval workflows are relevant, Invoice Software 2025: AI-Ready AP & Billing Guide. provides additional educational context on invoice processing and finance automation.
Companies can also examine the broader relationship between customer records and invoicing through Sync Sales to Cash, which covers how CRM and invoicing software connect sales activity with billing processes. Accurate ERP integrations can help finance teams maintain consistent records across job costing, accounts receivable, and the general ledger.
Improving Project Billing and Collections
Contractors can improve visibility by establishing regular billing reviews, tracking unbilled completed work, and comparing project forecasts with approved customer billing schedules. They should also review outstanding invoices and confirm that customer payments are applied to the correct accounts and transactions.
AR Automation Software can support invoice follow-ups and payment matching, helping finance teams improve collection visibility. The collections process helps prioritize overdue invoices and coordinate customer communication, while cash application matches incoming payments to the appropriate invoices and supports accurate receivables records.
The Hyperbots Platform uses AI and ERP integration to automate finance and accounting tasks. When evaluating these tools, contractors should focus on whether connected workflows improve transaction accuracy, reduce manual reconciliation, and provide timely information for billing and project reviews.
Summary
Sage 100 Over Under Billing helps contractors compare customer billings with revenue earned on a project. Overbilling occurs when billings exceed earned revenue, while underbilling occurs when earned revenue exceeds billings. By calculating the difference, reconciling job costs and invoices, and reviewing billing schedules regularly, finance teams can improve cash flow planning, strengthen financial reporting, and make better-informed project decisions.