Want to terrify yourself, carefree 20-something? Divide 1 million by 40 — the number of years until retirement — and you’ll see a nice round 25,000. That’s how much, *in dollars*, you’d need to save each year if you were stuffing money under a mattress to save your $1 million retirement nest egg. Thankfully, this is not how you save for retirement.

“The calculation of ‘I need $1 million dollars by 65, so I’ll divide by 40 . . . is dramatically off,” said Antwone Harris, a certified financial planner with Charles Schwab in the District. “It’s not accounting for compounding interest or rates of return.”

But those compounding interest rates mean one complicated thing: You must invest your savings as soon as possible. Why? According to Ameriprise Financial, waiting even one year can have dramatic effects. If you invest $5,000 every year beginning at age 30 instead of 31, you will have $109,000 in additional savings, assuming an 8 percent compounded annual interest rate.

So how much should you invest? What will you need for retirement? And how important is it to start investing every spare penny you make in your 20s? Too many factors go into the calculation to generalize (and there’s not enough space here to explain a complex mathematical formula), so we used CNN Money and Charles Schwab Moneywise retirement calculators to get ballpark figures of what you should be saving. Read. Weep. Then invest.

**How much will I need to invest each year for retirement?**

**Low figure:** It’s assumed that you’ll need 80 percent of your pre-retirement income when you retire at 65. Let’s say you make $50,000 a year. If you’re 25 and have no savings, CNN Money says you should be saving $4,550 annually, adjusted for 2.5 percent inflation. (This calculator assumes you will be receiving Social Security benefits. More good news: Some experts do not think Social Security will exist in 40 years.)

**High figure:** Charles Schwab MoneyWise Calculator offers a higher figure. If you’re 25 and plan to retire at 65 with 80 percent of your pre-retirement income, and expect to receive Social Security benefits, you need to save $6,900 annually.

**How much will I need for retirement? ** CNN Money assumes you will need $1.9 million ($572,283 in today’s dollars) to retire at 65 years old, with a life expectancy of 85. Charles Schwab estimates you will need $1.8 million in future dollars.

**What should I save each paycheck?** If you’re paid every two weeks, you should save $175 to $275 each pay period to meet the estimated goal.

**How much will I need to invest each year for retirement?**

**Low figure:** You’ll need 80 percent of your pre-retirement income when you retire at 65. You make an annual salary of $50,000. If you’re 35 with no savings, CNN Money recommends saving $6,650 annually, adjusted for 2.5 percent inflation. (This calculator assumes you will be receiving Social Security benefits.)

**High figure:** Charles Schwab MoneyWise Calculator says if you’re 35 and plan to retire at 65 with 80 percent of your pre-retirement income, you need to save $11,200 annually.

**How much will I need for retirement: ** CNN Money assumes you will need $1.4 million or $577,458 in today’s dollars to retire at 65 years old. Charles Schwab estimates you will need almost $1.3 million in future dollars.

**What should I save each paycheck?** If you’re paid every two weeks, you should save $255 to $430 each pay period to meet the estimated goal.

**How much will I need to invest each year for retirement?**

**Low figure:** You’ll need 80 percent of your pre-retirement income when you retire at 65. Let’s say your annual salary is $50,000. If you’re 45 and haven’t saved anything, shame on you. Still, CNN Money suggests you should be saving $9,850 annually, adjusted for 2.5 percent inflation. (This calculator assumes you will be receiving Social Security benefits.)

**High figure:** Charles Schwab MoneyWise Calculator offers a higher figure. If you’re 45 and plan to retire at 65 with 80 percent of your pre-retirement income, and are counting on Social Security, you need to save $20,300 annually. This number is very difficult to achieve on a $50,000 salary.

**How much will I need for retirement: ** CNN Money assumes you will need a total of $1.1 million ($582,681 in today’s dollars) to retire at 65 years old. Charles Schwab estimates you will need $1 million in future dollars.

**What should I save each paycheck?** If you’re paid every two weeks, you should save $378 to $780 each pay period. Eek!

**THE BOTTOM LINE:**This is painful. Seeing these numbers might make you cry (particularly if you’re 45 or older.) The key is to start saving now. If you’re company has a 401(k) plan, enroll immediately and contribute enough to meet your company’s match. If you’re young, build an aggressive stock portfolio with the help of a financial adviser.