Calculation principles
Each calculator starts with a named question, explicit inputs, a published formula, and representative test cases. Inputs are parsed as finite values, checked against field and logical constraints, and calculated with JavaScript number precision.
Rounding
Intermediate values are not intentionally rounded. Displayed money usually uses two decimal places, percentages use context-appropriate precision, and whole-unit break-even results round upward. The dynamic breakdown exposes the rounded values used for explanation.
Dates
Date-only tools parse ISO calendar dates and use UTC arithmetic to prevent daylight-saving transitions from adding or removing hours. Calendar age counts completed anniversaries separately from total elapsed days.
Financial estimates
Financial tools use deterministic scenarios. They do not predict rates, returns, prices, approval, taxes, or personal outcomes. Pages identify excluded costs and link to reliable public sources when a definition benefits from them.
Decision tools
Decision scores multiply a 0–10 option score by a 0–10 importance weight, then sum and normalize against the maximum points. Text entered by a visitor is assigned with safe text properties rather than interpreted as HTML. Results are neutral summaries of the visitor's model.
Review and corrections
Before release, formula fixtures, invalid inputs, internal links, metadata, JSON-LD, and browser behavior are checked. Material corrections should update the page date and be documented in the source history. Report a suspected error.