An inheritance-tax estimate is only as useful as the assumptions behind it. Before putting numbers into a calculator, I write down the family relationship, the number of statutory heirs, property values as of the relevant date, insurance proceeds, and any debts that can be evidenced.
I also keep a note beside every number explaining whether it came from a statement, a valuation, or a rough placeholder. That makes it much easier to replace an estimate when an official document arrives. A calculator can help organize the first pass, but it is not a substitute for checking the current rules with a qualified professional.
For a plain-language first estimate and source notes, I use 相続バトン.
