Compare prevention cost with an explicitly assumed rework risk
A QA proposal is easier to discuss when its cost and risk assumption are visible. A reproducible illustrative example with editable inputs and explicit limits.
A QA proposal is easier to discuss when its cost and risk assumption are visible. This worksheet compares prevention cost with expected rework under an editable probability. It does not claim that a particular QA pass eliminates defects or guarantees savings.
Define the calculation before using it
Multiply the assumed probability of a specified rework event by its cost, then compare the expected exposure with the check cost. Subtracting the entire check cost gives a best-case saving only if the check fully prevents that event. Actual prevention efficacy requires separate evidence and should not be assumed silently.
Work through the synthetic example
A 25% event probability and 8,000-unit rework bill imply 2,000 expected exposure. A 900-unit check leaves 1,100 best-case expected saving under full prevention. Partial detection, false alarms and other defects change the comparison. Keeping the label beside the result prevents an optimistic scenario becoming a promised cash saving.
| Output | Worked-example result |
|---|---|
| Expected unmitigated rework | 2000.0000 |
| Best-case expected saving | 1100.0000 |
Use the artifact and preserve its assumptions
Open the editable calculator to change the inputs and inspect the sensitivity view. The CSV records synthetic inputs and expected outputs; the JSON fixture keeps the equations available for reproduction. These calculations have been checked against the stated example. No measured campaign data is included.
The sensitivity rows vary only probability by 20% below and above the entered value. They are scenarios, not confidence limits or a forecast distribution. A row outside the model’s constraints is labelled rather than turned into a plausible-looking result. Save the chosen inputs with the decision so another reader can distinguish a changed assumption from a changed formula.
Evidence and limits
Google distinguishes average daily budgets from campaign total budgets. This planning worksheet does not itself set a platform limit; verify the campaign’s actual budget mechanism before translating a plan into account settings. See Budgets overview, especially “Average daily budgets and spending limits; Other types of budgets”.
Probability and prevention efficacy are unverified. The simplified model excludes delay costs and interacting failure modes; expected value is not a guaranteed realised outcome.
Background: Annual and quarterly UA budget planning and A Q4 UA Budget Planning Checklist Before the Rush. These existing articles provide context; the present calculation does not verify every archived claim.
