Percentage of Completion Method (PCM) for Contractors: IRC 460 Rules, Calculations, and Look-Back Interest

The percentage of completion method (PCM) is the IRS’s default method for recognizing income on long-term construction contracts. If your construction company has average annual gross receipts above the IRC 448(c) threshold ($31 million for 2025, adjusted annually for inflation), you are required to use PCM for contracts that will not be completed in the same tax year they are entered into. Getting the calculation wrong in either direction creates problems: understate your completion percentage and you defer too much revenue (triggering an IRS adjustment plus interest), overstate it and you accelerate income you did not need to report yet. This article walks through the mechanics of PCM under IRC 460, the elections that modify it, and the look-back interest computation that reconciles estimated and actual results when the contract is done.

What’s the cost-to-cost method, and how does it work?

The cost-to-cost method is the formula prescribed by IRC 460(b)(1)(A) for measuring the percentage of a contract that has been completed during the tax year. The formula is straightforward: divide the cumulative allocable contract costs incurred through the end of the tax year by the total estimated allocable contract costs at completion. Multiply the resulting percentage by the total contract price to get cumulative revenue, then subtract prior-year cumulative revenue to arrive at the current year’s recognized revenue.

In notation: Completion % = Cumulative Costs Incurred / Total Estimated Costs. Current-Year Revenue = (Completion % x Total Contract Price) minus Revenue Recognized in Prior Years.

The formula depends on two inputs, and both require judgment. Cumulative costs incurred is the easier number because it comes from the job costing system, but only if that system is capturing all allocable contract costs accurately. Total estimated costs at completion is a forward-looking estimate that must be updated for change orders, scope modifications, material price changes, productivity variances, and any other factor that changes the expected cost to finish the work. If the estimate is stale (still reflecting the original bid number rather than the current cost reality), the completion percentage is wrong and the revenue recognition is wrong.

The revenue figure that PCM produces is the amount recognized for tax purposes regardless of how much the contractor has billed or collected. A contractor who is 60% complete and has billed only 40% of the contract still recognizes 60% of the revenue. Conversely, a contractor who is 60% complete and has billed 80% recognizes only 60%. The WIP schedule reconciles these differences through the over-billed and under-billed positions on the balance sheet.

Which costs are “allocable contract costs” under IRC 460?

IRC 460(c) defines allocable contract costs as all costs that are allocable to the contract under the rules for extended-period long-term contracts. In practice, this means the contractor must include direct costs (materials, direct labor at the burdened rate, subcontractor costs, equipment charges, permits) and a share of indirect costs that benefit the contract. The indirect cost categories that must be allocated include: insurance, taxes (payroll taxes, property taxes on equipment), depreciation on equipment and facilities used for the contract, repairs and maintenance of project equipment, engineering and design costs, and contract administration costs.

Costs that are not allocable to the contract include general and administrative expenses that do not benefit contract performance (marketing, executive compensation not related to contract supervision, office rent for a headquarters not involved in contract execution), bidding and proposal costs on contracts not yet awarded, and research and development costs not related to a specific contract. The line between allocable indirect costs and nonallocable G&A can be blurry, and the IRS has challenged contractors who exclude too many indirect costs from the allocation pool (which deflates cumulative costs incurred, understates the completion percentage, and defers revenue recognition).

For a deeper look at which costs are tracked to each project and how the allocation methods work, see our guide on construction job costing and accounting methods.

When is PCM required, and when is it optional?

PCM is required when two conditions are met. First, the contract must be a “long-term contract,” defined under IRC 460(f)(1) as any contract for the manufacture, building, installation, or construction of property that is not completed within the tax year in which the contract is entered into. Second, the contractor must have average annual gross receipts above the IRC 448(c) threshold for the three preceding tax years ($31 million for 2025). If both conditions are met, PCM is mandatory for those contracts. There is no election to use another method.

Contractors below the gross receipts threshold have a choice. They can use the completed-contract method (which defers all revenue and cost recognition until the contract is complete), the cash method, or the accrual method, depending on their overall accounting method. They can also elect PCM voluntarily. There are reasons to do so: PCM produces smoother income recognition across years, which can be advantageous for bonding capacity and financial statement presentation, and it avoids the large income spike that hits in the completion year under the completed-contract method. The tradeoff is that PCM typically accelerates income relative to the completed-contract method, so the contractor pays tax sooner.

One important nuance: the gross receipts threshold is tested at the entity level (and aggregated with related entities under the common-control rules). A contractor who has been below the threshold for years and then crosses it (through organic growth or acquisition) becomes subject to PCM for new contracts entered into in the year the threshold is crossed. This is an automatic accounting method change for the affected contracts, and the contractor must use PCM from the first year the threshold is exceeded. Going the other direction (dropping below the threshold) allows the contractor to stop using PCM for new contracts, but existing contracts already on PCM generally remain on PCM until completed.

For how the choice of accounting method interacts with entity structure decisions, including the aggregation rules that determine which related entities’ receipts count toward the threshold, see the entity structure guide.

What’s the 10% method and why elect it?

The 10% method under IRC 460(b)(1)(A) allows a contractor to defer all income recognition on a contract until the tax year in which at least 10% of the total estimated allocable contract costs have been incurred. In effect, the contract is not treated as “entered into” for PCM purposes until the 10% cost threshold is reached. Once it is reached, PCM applies normally from that point forward, and the contractor recognizes revenue based on the cumulative completion percentage (including the costs incurred before the 10% threshold was crossed).

The election is useful when a contract has a long mobilization period or front-loaded costs that are not representative of actual construction progress. A highway project, for example, might involve months of mobilization, utility relocation, and permitting before construction begins. If the contractor incurs 3% of total estimated costs during the mobilization phase, the 10% method defers all revenue recognition until actual construction is underway and a more meaningful percentage of costs has been incurred.

The 10% method is an annual election made on a contract-by-contract basis. It is not an all-or-nothing choice across the contractor’s entire portfolio. The election is made by reporting the contract consistently on the tax return, and it does not require a separate statement to the IRS.

How does look-back interest work under IRC 460(b)(2)?

Look-back interest is the reconciliation mechanism built into PCM. During the life of a contract, the contractor estimates total costs each year and recognizes revenue based on those estimates. When the contract is completed and total actual costs are known, those estimates are almost always wrong (usually not by much, but sometimes significantly). The look-back method under IRC 460(b)(2) requires the contractor to recompute what should have been reported in each prior year using the actual total cost figure, calculate the tax difference between what was actually reported and what should have been reported, and pay or receive interest on that difference.

The mechanics work like this. For each year the contract was open, the contractor recalculates the completion percentage using actual total costs (instead of the estimated total costs used on the original return). The difference in taxable income is computed for each year, and the resulting tax overpayment or underpayment for each year accrues interest at the federal underpayment rate from the due date of that year’s return to the due date of the return for the completion year. If the contractor underestimated costs (actual costs exceeded estimates), the contractor overreported income in the early years and is owed interest. If the contractor overestimated costs (actual costs came in under estimates), the contractor underreported income in the early years and owes interest.

The computation is reported on Form 8697 (Interest Computation Under the Look-Back Method for Completed Long-Term Contracts), which is filed with the tax return for the year the contract is completed.

There is a de minimis exception: the look-back computation is not required for a contract if the cumulative taxable income (or loss) reported under PCM in each prior year is within 10% of the amount that would have been reported using actual total costs. This spares contractors from filing Form 8697 on contracts where the estimates were reasonably accurate.

How does simplified cost-to-cost work for residential?

IRC 460(e) provides two special rules for residential construction. First, a “home construction contract” (defined as a contract where 80% or more of the estimated total contract costs are reasonably expected to be attributable to the construction of dwelling units in buildings containing four or fewer dwelling units, and improvements to real property directly related to those units) is exempt from the PCM requirement entirely, regardless of the contractor’s gross receipts. The contractor can use the completed-contract method, the cash method, or another permissible method.

Second, for contractors who are otherwise required to use PCM but have contracts that do not qualify as home construction contracts yet involve residential construction, IRC 460(e)(1) allows a simplified cost-to-cost method. Under the simplified method, the contractor is not required to include certain indirect costs in the allocable contract cost pool. The practical effect is that the completion percentage is calculated using a narrower cost base, which can slow down revenue recognition relative to the standard PCM calculation.

What’s the 70/30 method for home construction contracts?

For home construction contracts that are exempt from mandatory PCM under IRC 460(e)(1), the contractor can elect a hybrid approach: 70% of the contract income is recognized using PCM, and the remaining 30% is deferred and recognized under the completed-contract method (recognized entirely in the year the contract is complete). This is sometimes called the “70/30 method” or the “alternative minimum tax method” because it was originally designed to address AMT preferences.

The 70/30 method is a middle ground. It provides smoother income recognition than the pure completed-contract method (which causes an income spike in the completion year) while still deferring more income than full PCM. The 30% deferred to the completion year often consists disproportionately of profit (because costs are front-loaded and the final 30% of revenue recognized at completion has relatively little cost against it), which creates a planning opportunity for the completion year.

The election is made by reporting the contract consistently on the tax return. It applies to all home construction contracts, so the contractor cannot apply 70/30 to some home contracts and completed-contract to others. A contractor who elects 70/30 and later wants to switch to full PCM or full completed-contract must file a change of accounting method (Form 3115).

How does PCM interact with retainage, billing, cash flow?

PCM recognizes revenue based on costs incurred, not on billing or cash collection. This creates three common mismatches between taxable income and cash flow.

First, PCM revenue can exceed billings. A contractor who is 60% complete but has only billed 45% of the contract recognizes 60% of the contract price as revenue for tax purposes. The contractor pays tax on revenue it has not yet billed, let alone collected.

Second, retainage withheld from progress payments reduces cash received but does not reduce PCM revenue. A contractor who is 60% complete and has been billed 60%, but with 10% retainage held on every billing, has collected only about 54% of the contract price while recognizing 60% for tax. For the tax treatment of retainage specifically, see our retainage accounting guide.

Third, cost overruns in the final year can create a look-back interest benefit, but the cash flow damage of the overrun itself is immediate. A contractor who underestimated total costs will have accelerated revenue in the early years (because the completion percentage was overstated), and the look-back interest computation will produce a refund of interest. But the refund is modest compared to the lost profit margin.

The practical implication: PCM contractors need to manage cash flow separately from tax income. The WIP schedule is the tool that reconciles billings, costs, and PCM revenue, and it should be reviewed quarterly to identify contracts where the billing position is falling behind the completion percentage.

How does PCM interact with equipment depreciation?

Equipment depreciation under IRC 179 and bonus depreciation is a separate deduction from the PCM income calculation. Depreciation on equipment used on a specific contract is an allocable contract cost (it enters the cost-to-cost numerator), but the Section 179 deduction and bonus depreciation are deducted at the entity level, not at the contract level. A contractor on PCM can still take a full Section 179 deduction on new equipment in the year of purchase, reducing overall taxable income even if PCM produces significant contract-level revenue.

This is an important planning point. A contractor who knows that PCM will produce substantial revenue in a given year (because several large contracts are nearing completion) can offset that revenue with equipment purchases and Section 179 deductions, contractor tax deductions for vehicles, insurance, and other business expenses, and retirement plan contributions. The PCM revenue is locked in by the cost-to-cost formula, but the deductions that offset it are within the contractor’s control.

How do change orders factor into PCM calculations?

Approved change orders increase the total contract price and (usually) the total estimated costs. Both numbers feed the PCM formula, so an approved change order adjusts the completion percentage in both the numerator (if additional costs have been incurred) and the denominator (if estimated total costs increased). The net effect depends on whether the change order is profitable (which slows down the completion percentage slightly) or a break-even scope addition (which has minimal effect).

Unapproved or disputed change orders create a conservative-versus-aggressive judgment call. The costs are real and must be included in the cost-to-cost numerator. The revenue is uncertain. The safer treatment is to include the costs but not the unapproved revenue, which temporarily depresses the project’s apparent profitability and completion percentage. For a full discussion of change order management and revenue recognition, see our dedicated guide.

What should I do next?

PCM is not something a contractor can set up once and forget. Every year the contract is open, the completion percentage depends on an accurate cost-to-cost ratio, which requires current job costing and a realistic total cost estimate. In the completion year, the look-back computation adds a layer of reconciliation. If you are a contractor above the gross receipts threshold (or approaching it), or if you are voluntarily on PCM and want to confirm you are calculating it correctly, a review of your PCM calculations, WIP schedule, and look-back interest exposure is the place to start.

• Construction job costing and accounting methods, covering how the job cost system feeds the PCM formula
• Construction contractor tax deductions and expenses, including which costs are allocable to contracts and which are deducted separately
• Construction equipment depreciation and Section 179, the deductions that offset PCM revenue at the entity level
• Construction entity structure: LLC vs S-Corp, including how the gross receipts threshold is tested across related entities
• Construction retainage accounting and tax treatment, the cash flow mismatch between retainage withheld and PCM revenue recognized
• Construction change order management and revenue recognition, how pending and approved change orders affect the PCM calculation

Related guides:

• Construction Change Order Management Revenue Recognition
• Construction Contractor Tax Deductions Wip Accounting
• Construction Entity Structure Llc Scorp Qbi Deduction
• Construction Equipment Section 179 Bonus Depreciation
• Construction Insurance Bonding Surety Tax Treatment

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.