Liz Weston: 9 money numbers you need to know

Your doctor needs to know certain numbers to judge your physical health, such as your weight, your blood pressure and your cholesterol levels.

Similarly, you need to know certain numbers to monitor your own financial health, including:

AFTER-TAX INCOME AND ‘MUST-HAVE’ EXPENSES

Your after-tax income is your gross income minus the taxes you pay (federal, state and local income taxes, plus Social Security and Medicare taxes). If you get a steady paycheck, you can use your latest pay stub to calculate this figure. Otherwise, check your most recent tax return.

Divide your after-tax income by the number of hours you worked to earn it. That gives you a rough idea of how much time you’re trading when you buy something. For example, if you make $20 an hour after tax and something costs $100, you have to work five hours to afford it. Knowing that figure can help you make more conscious money decisions.

Your after-tax income also is the basis for the 50/30/20 budget, a spending plan that helps you balance current expenses, debt payments and savings. That budget suggests limiting your essential or must-have expenses — shelter, utilities, transportation, food, insurance, minimum loan payments and child care needed to work — to 50% of after-tax income. Wants, such as vacations and dining out, make up 30%. That leaves 20% for savings and extra debt payments.

Capping must-haves can help you survive a job loss or other financial setback. You also can use the limits to determine if you can afford a new loan payment. If the payment pushes your must-haves over the 50% mark, the answer may be no.

LIFETIME INCOME AND NET WORTH

You can access your Social Security statement, including your lifetime earnings history, by signing up at socialsecurity.gov/myaccount. Add up your annual...