Software Maintenance Cost Calculator
Estimate a year of maintenance from how much of the system changes.
In short
Estimate a year of maintenance from how much of the system changes.
Formula: ACT = (Code added + Code modified) ÷ Base size; Maintenance size = Base size × ACT; PM = 2.94 × Maintenance size^(0.91 + 0.01 × ΣSF) × ΠEM; Cost = PM × Loaded cost per person-month
What this calculator does
Annual change traffic is computed from code added and modified against the base size, and the maintained size is estimated with the same post-architecture equation the development model uses.
Use it to turn Currency, Size of the existing system, Code added in a year, Code modified in a year, and the other shown inputs into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this professional & industry calculation.
Inputs and what they mean
- Currency
- — Amounts are shown in the currency you pick. No exchange rate is applied..
- Size of the existing system
- — Thousands of source lines already in production..
- Code added in a year
- — Thousands of source lines added..
- Code modified in a year
- — Thousands of source lines modified..
- Sum of the five scale factors
- — Your own ratings for precedentedness, flexibility, risk resolution, team cohesion and process maturity. 18.97 is the published nominal sum..
- Product of the effort multipliers
- — Multiply your rated effort multipliers together; 1 means nominal..
- Loaded cost of one person-month
- — number value.
How to use it
- Enter your own figures — the calculator never fills in a rate, price or benchmark for you.
- Press Calculate to see the result.
- Read the formula, variables, assumptions and source below the result before you rely on it.
Formula
ACT = (Code added + Code modified) ÷ Base size; Maintenance size = Base size × ACT; PM = 2.94 × Maintenance size^(0.91 + 0.01 × ΣSF) × ΠEM; Cost = PM × Loaded cost per person-month.
Inputs used: Currency, Size of the existing system, Code added in a year, Code modified in a year, Sum of the five scale factors, Product of the effort multipliers, Loaded cost of one person-month.
Edge handling: Size of the existing system is required.; Size of the existing system cannot be negative.; Size of the existing system must be no more than 1000000000.; Code added in a year is required.; Code added in a year cannot be negative..
Worked example
100 KSLOC system with 15 KSLOC of annual change
- Start with Currency: USD, Size of the existing system: 100, Code added in a year: 6, Code modified in a year: 9, Sum of the five scale factors: 18.97, Product of the effort multipliers: 1.
- Apply the method: ACT = (Code added + Code modified) ÷ Base size; Maintenance size = Base size × ACT; PM = 2.94 × Maintenance size^(0.91 + 0.01 × ΣSF) × ΠEM; Cost = PM × Loaded cost per person-month.
- The published maintenance model: annual change traffic drives the maintained size.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this software maintenance cost calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: University of Southern California, Center for Systems and Software Engineering — COCOMO II model definition manual
Last reviewed:
Common questions
Where does this formula come from?
COCOMO II Model Definition Manual — post-architecture effort PM = A × Size^E × ΠEM with A = 2.94 and E = B + 0.01 × ΣSF (B = 0.91), and schedule TDEV = C × PM^(D + 0.2 × (E − B)) × SCED%/100 with C = 3.67 and D = 0.28. See the source link on this page.
What kind of calculation is this?
The published maintenance model: annual change traffic sets the maintained size, which is then estimated as effort and costed. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
What are its limits?
COCOMO II is a calibrated estimation model, not an exact prediction; its published accuracy is a range, not a point. Estimates are only as good as the size, scale factors and effort multipliers entered. Covers change-driven maintenance effort, not licences, hosting or support desks.
How do I use the Software Maintenance Cost Calculator?
Enter the required values for Currency, Size of the existing system, Code added in a year, Code modified in a year, Sum of the five scale factors, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Software Maintenance Cost Calculator use?
ACT = (Code added + Code modified) ÷ Base size; Maintenance size = Base size × ACT; PM = 2.94 × Maintenance size^(0.91 + 0.01 × ΣSF) × ΠEM; Cost = PM × Loaded cost per person-month The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
Can the Software Maintenance Cost Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Formula, source and verification
The published maintenance model: annual change traffic sets the maintained size, which is then estimated as effort and costed.
The question it answers: What will it cost to keep this system going for another year?
The formula
ACT = (Code added + Code modified) ÷ Base size; Maintenance size = Base size × ACT; PM = 2.94 × Maintenance size^(0.91 + 0.01 × ΣSF) × ΠEM; Cost = PM × Loaded cost per person-month
- Base — Size of the existing system
- (KSLOC). Thousands of source lines already in production.
- Add — Code added in a year
- (KSLOC). Thousands of source lines added.
- Mod — Code modified in a year
- (KSLOC). Thousands of source lines modified.
- ΣSF — Sum of the five scale factors
- (points). The organisation's own ratings.
- ΠEM — Product of the effort multipliers
- (factor). The organisation's own rated multipliers.
- c — Loaded cost of one person-month
- (currency). Employer cost of one person-month.
Units: KSLOC; person-months; currency.
What kind of calculation this is
Estimation model. This is a published estimation model. It produces an estimate, not a measured fact, and its accuracy depends on how well your situation matches the model.
Method
Annual change traffic is computed from code added and modified against the base size, and the maintained size is estimated with the same post-architecture equation the development model uses.
Assumptions built into the result
- Mathematical: Added and modified code are measured over the same year as the cost being estimated.
Figures this calculator will never guess for you
- No industry delivery rate, productivity figure, defect rate or cost per line is inserted.
- No optional component is filled in on the user's behalf.
- No default change traffic percentage is assumed.
Limitations
- COCOMO II is a calibrated estimation model, not an exact prediction; its published accuracy is a range, not a point.
- Estimates are only as good as the size, scale factors and effort multipliers entered.
- Covers change-driven maintenance effort, not licences, hosting or support desks.
Source and version
- Standard or reference
- COCOMO II post-architecture model — University of Southern California, Center for Systems and Software Engineering (COCOMO II Model Definition Manual — post-architecture effort PM = A × Size^E × ΠEM with A = 2.94 and E = B + 0.01 × ΣSF (B = 0.91), and schedule TDEV = C × PM^(D + 0.2 × (E − B)) × SCED%/100 with C = 3.67 and D = 0.28.)
- Published source
- University of Southern California, Center for Systems and Software Engineering — COCOMO II.2000
- Formula version
- Version 1
- Verification
- Reviewed against the cited source on
- How much weight the source carries
- Academic
- Applies to
- Currency
- Amounts stay in the currency you choose; no exchange rate is applied.
Cite this page
Free Calculator. (2026, September 16). Software Maintenance Cost Calculator. https://freecalculator.tech/tools/software-maintenance-cost-calculator
"Software Maintenance Cost Calculator." Free Calculator, 16 Sept. 2026, https://freecalculator.tech/tools/software-maintenance-cost-calculator.
Software Maintenance Cost Calculator — Free Calculator, https://freecalculator.tech/tools/software-maintenance-cost-calculator
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