Getting reliable answers from finance calculators
Most money calculators rely on a handful of standard formulas: the annuity formula for loan and EMI payments, compound growth for savings and investments, and simple percentages for tax and pricing. The formulas are exact, but the answer is only as good as the inputs. Use the interest rate from your actual offer letter, check whether it is quoted per year or per month, and remember that most projections assume the rate stays the same.
For investments, the expected return is a guess about the future. Try a cautious, a middle and an optimistic rate to see the range of outcomes rather than relying on a single number. For tax calculators, confirm the current rate for your product or region, because rates change.