Calculation integrity and input quality
Our engines are deterministic: the same valid inputs produce the same unrounded result. Decimal arithmetic is used where costs are added, multiplied, divided, and amortized. Only displayed values are rounded. Benchmark fixtures and boundary tests check mathematical behavior.
Input confidence answers a separate question: how much do you know about the numbers you entered? Each tool asks you to classify three groups of inputs as examples, informed estimates, or checked against your own bills, quotes, and records.
The groups receive 25, 65, or 100 points, and are averaged equally. Scores below 55 are rough; 55–74 moderate; 75–89 strong; 90–100 very strong. This is an editorial quality rubric, not a statistical confidence interval. Future resale and usage can still be uncertain after careful checking.
Choose a methodology
What every model leaves out
A useful estimate has boundaries. Each tool shows the costs it includes and the assumptions it holds constant. We do not infer legal eligibility, mechanical safety, tax treatment, future prices, or personal suitability from a formula.
Reference numbers are dated and labeled. User-entered prices usually fit your situation better than broad averages. Use a second scenario to check whether a reasonable change would reverse your conclusion.