To calculate loss of profit, take the revenue your business would have earned during the disruption, subtract the costs you would have spent to earn it, and subtract anything you actually did earn in its place. What’s left is the lost profit. The arithmetic is simple. The work is in the inputs: a defensible revenue projection, a clean split between costs that vanished and costs that kept running, and documentation strong enough to meet the legal standard courts apply before awarding damages.
The Core Formula
Lost profits equal lost revenue minus avoided costs, minus any substitute earnings. If your business would have generated $500,000 in revenue over the loss period, would have spent $350,000 on materials, labor, and other variable expenses to produce it, and earned nothing in its place, the lost profit is $150,000. That figure is sometimes called the contribution margin: revenue minus the costs that move in step with sales.
Claiming gross revenue as your loss is the fastest way to get a damages estimate thrown out. Revenue is not profit, and courts award profit. The whole point of the calculation is to isolate the margin you would have kept after paying to earn the money.
Which Costs Come Out, Which Stay In
Variable Costs Get Subtracted
When business activity stops, certain expenses stop with it. Raw materials you didn’t buy, shipping fees you didn’t incur, hourly labor you didn’t use, and sales commissions you didn’t pay all disappear alongside the lost revenue. Every one of these must come out of your lost-revenue figure. Leaving them in means claiming money you would have spent, not money you would have kept.
Semi-Variable Costs Get Split
Some expenses contain both a fixed baseline and a portion that scales with output. Utilities, maintenance, and supervisory labor typically behave this way. A factory’s electric bill doesn’t drop to zero when the production line stops, but it also doesn’t stay at full-capacity levels. Split each one, deduct the variable share, and leave the fixed share in the claim.
The longer the loss period, the more costs that looked fixed in the short term start behaving like variable ones. A six-month shutdown might mean terminating a lease or laying off salaried staff, converting formerly fixed obligations into avoidable expenses. Reassess the classification against the length of the disruption, not against how the accounting worked before it started.
Fixed Costs Stay In
Rent, insurance premiums, loan payments, and other obligations that continue regardless of revenue do not get subtracted. You’re still paying them during the disruption, so they represent real ongoing harm. Expect the opposing expert to argue that some of your fixed costs are actually variable, and be ready to defend each line item’s classification with evidence of how the cost actually behaved during the loss period.
Three Ways to Project the Lost Revenue
Before-and-After
Compare the business’s actual profit before the disruption to its actual profit during it. If a restaurant averaged $60,000 in monthly profit for two years before a fire and dropped to $15,000 per month while operating from a temporary location, the monthly loss is $45,000. This method fits established businesses with stable earnings histories and few outside variables. If a recession hit at the same time as the breach, the drop can’t all be pinned on the defendant, and the other side will press that point.
Yardstick
When your historical data is thin or the business was growing rapidly, compare the affected company to a similar unaffected one. The yardstick might be a competitor in the same market, a different branch of the same franchise, or an industry composite. If comparable stores grew 12% while yours flatlined after the disruption, that gap becomes the basis for damages. Finding a genuinely comparable business is the hard part; differences in location, management, product mix, or customer base all give the opposing side room to attack the comparison.
But-For Forecast Modeling
This method builds a financial model of what the business would have earned “but for” the harmful event. Rather than extending a historical trend line, it incorporates secured contracts, planned expansions, market growth rates, and operational changes already in motion. A company about to launch a new product line with signed distributor agreements and completed inventory purchases might project an additional $200,000 in annual revenue, then compare that trajectory to what actually happened.
Because but-for modeling involves more assumptions than the other two methods, courts hold it to a tighter evidentiary standard. Every input needs documentation, not management optimism.
The Records That Make the Number Defensible
A lost-profit claim lives or dies on its paper trail. The most important documents are your historical income statements and profit-and-loss reports, ideally covering three to five years before the disruption. These establish the baseline: what the business actually earned, season by season, so an analyst can project what it should have earned going forward.
Reconcile those internal financials against your federal tax returns. Corporations file Form 1120, which reports total income, deductions, and taxable income on a single document.1Internal Revenue Service. About Form 1120, U.S. Corporation Income Tax Return Sole proprietors report business earnings on Schedule C attached to the personal return.2Internal Revenue Service. Topic No. 407, Business Income Tax returns matter because they’re filed under penalty of perjury. Opposing counsel will compare your claimed earnings trajectory to what you told the IRS, and any gap undermines the whole claim.
Beyond the financials, gather every contract, purchase order, and letter of intent that shows revenue you had locked in or were likely to receive. A signed two-year supply agreement the breach killed is far more persuasive than a forecast built on optimism. Detailed sales ledgers, inventory records, and customer correspondence fill in transaction volume and seasonal patterns. Organize everything chronologically in monthly or quarterly periods, so fluctuations show up rather than getting buried in annual averages.
Industry benchmarks strengthen the claim by showing your projections aren’t outliers. Published financial-ratio databases compile data from tens of thousands of businesses sorted by industry code, presenting median profit margins and expense ratios. When your internal numbers align with industry medians, arguing that your projections are inflated becomes much harder.
Adjustments That Change the Final Number
Substitute Earnings and the Duty to Mitigate
You can’t sit idle after a breach and claim every dollar as if nothing could have been done. The law requires reasonable steps to minimize losses. If a supplier breaks a contract, you’re expected to find a replacement at a reasonable cost rather than shutting down and billing the original supplier for the full revenue shortfall. Any earnings you make through substitute arrangements, or could have made through reasonable effort, get subtracted from the award.
Reasonable is the operative word. You don’t have to accept a demeaning alternative, pivot to a different business model, or spend disproportionate money chasing replacement revenue. But you do have to try. Document the calls you made, the proposals you sent, and the substitute deals you pursued. Those records matter almost as much as the ones supporting the original loss.
Discounting Future Losses to Present Value
When the claim covers future lost profits, meaning earnings the business would have made in years that haven’t arrived yet, those dollars need to be discounted to present value. A dollar received today is worth more than a dollar five years from now because today’s dollar can be invested. A court award paid now for losses that would have trickled in over a decade overcompensates the plaintiff unless the future amounts are adjusted downward.
The discount rate is where most of the courtroom fighting happens. A higher rate produces a smaller present-value number and favors defendants. A lower rate produces a larger one and favors plaintiffs. Common starting points include the risk-free Treasury rate, the company’s weighted average cost of capital, or a build-up rate that layers risk premiums on top of a base rate. Even a one-percentage-point difference can shift a ten-year damage figure by six figures.
Prejudgment Interest
Between the date of loss and the date of judgment, the money you should have earned had time value you never captured. Prejudgment interest bridges that gap by adding interest to the award for the intervening period. Rates and rules vary significantly by jurisdiction. Some states set a fixed statutory rate, others tie the rate to a published index, and the percentages range from single digits to the mid-teens. In some jurisdictions the interest accrues automatically once liability is established; in others the court has discretion over whether to award it at all. On a multi-year claim, the interest component alone can rival the underlying profit figure, so factor it into the model from the start.
What the Number Has to Prove in Court
Proximate Cause
Before the court considers your numbers at all, you have to prove the defendant’s specific act caused the profit loss. Many claims stall here. A business might have been declining before the breach, or an industry downturn might explain most of the revenue drop. The lost profits must flow directly from the defendant’s conduct, not from general market conditions, poor management decisions, or unrelated operational problems. The foreseeability test asks whether someone in the defendant’s position, at the time of contracting, would have reasonably anticipated that a breach could cause this type of financial harm.
Reasonable Certainty
Your damage figures must meet the standard of reasonable certainty. That doesn’t demand mathematical precision; courts recognize that projections involve estimation. It does mean the numbers can’t rest on speculation. A business with five years of stable $80,000 monthly profits claiming it would have earned $80,000 the month after a breach has strong footing. A business claiming it would have tripled revenue based on a pitch deck and no signed contracts does not.
Historical track records, secured contracts, binding purchase orders, and documented customer relationships all count as evidence of certainty. Vague growth plans, unsolicited expressions of interest, and management forecasts prepared after the litigation started generally do not.
Expert Testimony
In most lost-profit cases the numbers don’t speak for themselves. A forensic accountant or financial economist presents them, explains the methodology, and defends the assumptions on cross-examination. Federal courts evaluate this testimony under Federal Rule of Evidence 702, which allows expert opinions only when the expert’s specialized knowledge will help the jury and the methodology is reliable.3Office of the Law Revision Counsel. Federal Rules of Evidence Rule 702 – Testimony by Experts The reliability inquiry was shaped by the Supreme Court’s decision in Daubert v. Merrell Dow Pharmaceuticals.
Courts routinely exclude expert testimony when the methodology doesn’t fit the facts, such as using the before-and-after method on a business with wildly erratic pre-breach earnings, or applying a yardstick comparison to a company with no genuinely comparable peers. The admissibility fight focuses on the method itself, not the final dollar figure, which means picking the right expert and the right methodology matters as much as the underlying financial data.
Two Boundaries Worth Knowing
New Businesses
Startups and recently launched businesses face an extra hurdle because they lack the operating history that anchors most calculations. Courts historically applied a blanket rule barring new businesses from recovering lost profits, on the theory that any projection was inherently speculative. That rigid approach has largely been abandoned. The modern trend treats business age as an evidentiary issue rather than an automatic disqualifier: a startup still has to prove projected profits with reasonable certainty, but it isn’t turned away at the door for being new.
The practical question becomes what evidence substitutes for historical financials. Franchisees often point to the earnings of comparable franchise locations, since each unit operates from a similar business model with documented performance data. Other startups have succeeded by presenting the defendant’s own pre-litigation projections; if the defendant evaluated the business opportunity and projected specific earnings before the dispute arose, those numbers carry weight precisely because they were created without litigation incentives. Market studies, signed customer commitments, and industry data can also fill the gap, though each needs to be specific enough to connect to a concrete profit figure.
Taxes on the Award
Lost-profit awards and business-interruption insurance proceeds are generally taxable as ordinary income. The IRS treats damage payments the same way it would have treated the income they replace. Since the profits you lost would have been taxable business income, the award that compensates for them is taxable too, under the broad definition of gross income as “all income from whatever source derived.”4Office of the Law Revision Counsel. 26 U.S. Code 61 – Gross Income Defined This applies whether the payment comes from a court judgment, a settlement, or an insurance policy covering lost business income.
The tax hit can be large enough to affect settlement negotiations. If your actual lost profit was $300,000 and your effective tax rate is 30%, a $300,000 settlement leaves you with $210,000, less than what you would have netted on the original profits after tax. Some plaintiffs negotiate for a gross-up to cover the tax impact; defendants resist that as overcompensation. Either way, factoring taxes in before accepting a number prevents a surprise the following April.