Guides

Longer explanations behind our most-used calculators and tools, each with real numbers you can check yourself.

• How Mortgage Amortization Works

  Amortization is how a fixed mortgage payment pays off the loan over time. The payment stays the same, but the share going to interest shrinks every month while the share paying down your balance grows. Here is how that works, with real numbers.

• Compound Interest vs. Simple Interest Explained

  Simple interest is paid only on the money you put in. Compound interest is also paid on the interest you have already earned. Over a year or two the difference is pocket change. Over decades it is the main reason long-term saving works.

• How to Calculate Your GPA

  A grade point average turns letter grades into one number. The basic idea is the same everywhere: convert each grade to points, weight by credits if your school uses them, and divide. What changes between schools is the scale and whether harder classes count extra.

• What Makes a Password Strong

  A strong password is one an attacker cannot guess in any reasonable time. That depends mostly on how many possible passwords yours could have been, which comes down to length and true randomness, not clever substitutions.