About this tool
A single-number estimate hides uncertainty. This calculator offers three techniques and shows every formula so you can defend the result. Three-point (PERT) estimation takes optimistic, most likely and pessimistic hours per task, computes E = (O + 4M + P) ÷ 6 and SD = (P − O) ÷ 6, and gives approximate 68% and 95% ranges for the total. Work breakdown builds the estimate bottom-up from test case count, design and execution time per case, execution cycles, re-testing, setup, coordination and a contingency buffer. The percentage-of-development method is a quick top-down cross-check using a ratio you calibrate from your own history. All three convert hours into person-days and calendar days for your team size.
How to use it
- Choose a technique. Start with work breakdown when you know the scope in test cases, and PERT when you are estimating activities with real uncertainty.
- Enter your numbers. For PERT, add one row per activity; each row shows its own expected value and standard deviation.
- Review the breakdown, adjust assumptions such as cycles or buffer, then copy the summary into your test plan.
Test Estimation Calculator FAQ
Why does PERT weight the most likely value by 4?
PERT models each task with a beta distribution whose mean is approximately (O + 4M + P) ÷ 6. The weighting keeps the estimate close to the most likely value while still pulling it towards a long pessimistic tail, which is typical for testing work that depends on defect counts and environment stability.
How is the total standard deviation calculated?
Variances add, standard deviations do not, so the total SD is the square root of the sum of each task’s SD squared. This assumes the tasks vary independently. If one risk, such as an unstable environment, affects every task, the real spread is wider.
What percentage of development effort should testing be?
There is no universal figure. It depends on risk, domain, regulation and automation maturity. Use the ratio from your own completed projects (actual test hours divided by actual development hours) and compare it with a bottom-up estimate.