Software Maintenance Cost Calculator
Estimate a year of maintenance from how much of the system changes.
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.
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
Worked example
100 KSLOC system with 15 KSLOC of annual change
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
Results depend entirely on the figures you enter and are rounded for display. They are for general information and education, not professional advice.
Reference: University of Southern California, Center for Systems and Software Engineering — COCOMO II model definition manual
Last reviewed:
Common questions
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.
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