# Software Maintenance Cost Calculator

> Estimate a year of maintenance from how much of the system changes.

Page: https://freecalculator.tech/tools/software-maintenance-cost-calculator
Last reviewed: 2026-09-16

## 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

- 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..

## Inputs

- 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

## Worked example: 100 KSLOC system with 15 KSLOC of annual change

The published maintenance model: annual change traffic drives the maintained size.
1. 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.
2. 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.
3. The published maintenance model: annual change traffic drives the maintained size.

## 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.

## 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.

## Sources

- University of Southern California, Center for Systems and Software Engineering — https://csse.usc.edu/tools/cocomo/

## Cite this page

- APA: Free Calculator. (2026, September 16). Software Maintenance Cost Calculator. https://freecalculator.tech/tools/software-maintenance-cost-calculator
- MLA: "Software Maintenance Cost Calculator." Free Calculator, 16 Sept. 2026, https://freecalculator.tech/tools/software-maintenance-cost-calculator.
- Link: Software Maintenance Cost Calculator — Free Calculator, https://freecalculator.tech/tools/software-maintenance-cost-calculator