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Calculator guides

Understand the math and get more out of the tools.

Understanding Compound Interest

Compounding lets you earn interest on earlier interest.

How to Generate Strong Passwords

Choose a long, unique password for every account.

How to Calculate Return on Investment

Subtract the original cost from the final value, divide by the original cost, and multiply by 100.

A Guide to Simple Interest

Simple interest grows in a straight line because it is calculated on the original principal.

How to Estimate Take-Home Pay

Start with gross pay, subtract estimated withholding and post-tax deductions, then divide the remainder by the number of pay periods.

Mortgage Calculator Guide for Home Buyers

Your principal is your home price minus your down payment.

How to Estimate a Daily Step Goal

A step target is one way to plan activity.

How to Estimate Your Superannuation Balance

A projection combines your starting balance, future contributions, and an assumed return.

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Chinese Gender Calendar: How It Works and Is It Accurate?

Learn how the traditional Chinese Gender Calendar uses lunar age and conception month, and what a study of 2.84 million births found about its accuracy.