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Guides

Short, practical explanations of the formulas and methods behind AvyTool's calculators and text tools.

Learn the formula for percentage increase and work through a simple example.

Learn how to calculate percentage decrease between an original and a new value.

Understand markup as the amount added to a cost to reach a selling price.

See how a tax rate changes a pre-tax price and final total.

Understand the fixed-payment formula used for many installment loans.

Learn how total interest can be estimated from payments and principal.

Compare the basic formulas and understand how compounding changes growth.

Calculate growth when interest compounds 12 times per year.

Understand how calendar dates are compared to calculate age in completed years.

Learn the BMI formula and why it should be interpreted as a general screening measure.

Learn how elapsed calendar days are counted between two selected dates.

Learn how to calculate elapsed hours and minutes between two clock times.

Learn a simple method for estimating reading time from word count.

Calculate a tip, total bill, and per-person share with a simple formula.

Understand the simple whitespace-based method used by many word counters.