Reading
Guides
These articles use the same formulas as the calculators. They are explanations, not extra tools, and they do not invent bank quotes or state tax tables.
How percent change is computed here
The same ((new − old) ÷ old) × 100 formula used on the percentage calculator.
Markup versus margin
Why a 25 percent markup on cost is not a 25 percent margin.
How sales tax is added in this tool
Pre-tax and with-tax directions, with the rate you enter.
Compound interest versus simple interest
P × (1 + r ÷ n)^(n × t) compared with P × (1 + r × t).