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Cost Overrun Calculator
Cost overruns are the norm on rehab and construction projects. This calculator sizes the overrun impact against reserved contingency, flagging how much would come out of pocket and how it affects flip margins against ARV.
Projected actual cost
$201,250
Dollar overrun
$26,250
Beyond contingency (out-of-pocket)
$8,750
Profit eroded
$8,750
Margin vs ARV
53.20%
How the math works
Cost overrun is the norm, not the exception. Cosmetic flips typically run 5-10% over, medium rehabs 10-20%, heavy rehabs and new builds 15-30%+. A reserved contingency that equals the typical range keeps the project from bleeding into savings.
Drivers of overrun: scope creep, hidden damage behind walls, material price increases, permit delays extending carry cost. Lock scope tightly at contract signing. Don't add "while we're at it" items mid-project without formal change orders.
EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.
Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.
Learn more about our review process on the EveryCalc methodology page.
How this calculator works
What this page estimates
This Cost Overrun Calculator is built to give a quick, browser-based estimate for cost overrun. Cost overruns are the norm on rehab and construction projects. This calculator sizes the overrun impact against reserved contingency, flagging how much would come out of pocket and how it affects flip margins against ARV. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.
Calculation approach
The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.
Example workflow
For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.
Practical checks
- Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
- Run a low, base, and high case when the inputs are estimates.
- Check the related calculators below when the next decision depends on a different assumption.
How to interpret the cost overrun result
Best use
Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.
Cross-check
Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.
Watch for
Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.
This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.
Before relying on this cost overrun estimate
Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.
Confirm source numbers
Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.
Separate cash flow from total cost
A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.
Run conservative cases
Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.
Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.
How to Use
- Enter base budget (original contract price).
- Enter assumed overrun percentage based on scope.
- Enter contingency already reserved.
- Enter ARV or exit value for margin check.
Frequently Asked Questions
How much contingency should I reserve?
Cosmetic: 10%. Medium rehab: 15-20%. Heavy rehab: 20-30%. New construction: 15-20%. Increase contingency for projects with unknown conditions (historic homes, homes with water damage, older mechanical systems).
What drives overrun the most?
Scope creep and hidden damage. Plumbing behind walls, electrical surprises, and structural issues often add 15-25% to the base budget. Lock scope tightly and keep contractors on strict change-order discipline.
Should I build cost overrun into offer price?
Yes — experienced flippers back into max offer from ARV - rehab × 1.15 (or higher) - profit target - holding costs. Pricing with optimistic budgets leads to negative flips when reality kicks in.
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