By now, the dreadful truth probably has shown up in your mailbox — the yearend statements from brokerages and fund companies that show last year’s investment losses to the penny.

With this data in inescapable black and white, how can you use it to make future statements better? And how will your diminished worth affect long-term plans such as retirement?

Despite all the sophisticated planning tools available from computer programs, online calculators and financial advisers, most people wing it. In real life, the figure for what you need to save for something like retirement must take a back seat to what you can save. Most of us are just hoping for some good luck.

Still, it’s important to know whether you have any chance of meeting your goals, and things might not be as grim as you think.

One of the biggest questions facing people in or near retirement is how long their savings and investments will last once they start taking money out for living expenses.

Obviously, if your annual investment earnings are larger than your withdrawals, your money will last forever. But many people would be surprised to learn that their retirement money can last for decades even if they take out more than they earn.

According to a calculation by Ark Funds, a Baltimore mutual fund company, a portfolio returning a modest 4 percent a year will last for 42 years if only 5 percent is withdrawn each year. This is because only a small amount of principal is tapped with each withdrawal. It would last 14 years if 10 percent were withdrawn annually, and 10 years if 13 percent were taken out.

This means, of course, that at the end of these periods, all the principal would have been withdrawn as well as the investment gains, leaving nothing.

Increase the annual return to 6 percent and the fund will last forever so long as you take out less than 6 percent a year. Take 7 percent and it will last 34 years, take 10 percent and it will go for 16 years, and take 13 percent and it’ll last for 11 years.

Bump the annual return up to 8 percent and the portfolio will last 29 years if you take 9 percent, 21 years if you withdraw 10 percent and 13 years if you take 13 percent.

For a more sophisticated look at a portfolio’s endurance, use a program like Quicken 2003, the finance software, which takes taxes and inflation into account. Suppose you retire today, hope to live for 30 years and assume an annual investment return averaging 4 percent, inflation averaging 3 percent a year and that you’re in the 15 percent tax bracket.

Every $1,000 invested will then give you about $35 a year in after-tax income, with those withdrawals going up to counter inflation before all your money is gone in 30 years. Thus, a $1 million portfolio would provide you with $35,000 a year in actual buying power, for three decades.

Boost the investment return to 6 percent and every $1,000 will generate $44 a year. At 8 percent, it would be $54 a year.

The $49.95 Quicken 2003 Deluxe program is sold at computer stores and online at www.quicken.com. Microsoft Money 2003 Deluxe, a competing $55.95 program, has similar features. It’s at stores and can be bought at http://shop.microsoft.com.

With one of these programs and your yearend financial statements in hand, you can see whether your portfolio could be changed to boost expected investment returns while still reducing risks. (This also can be done with the free Asset Allocation tool at the Quicken site.)

Once you’ve listed your holdings in the program, it will tell what percentage is devoted to each asset class — big-company, small-company and foreign stocks, and so on.

The program will show how this portfolio would have performed in the past and describe how risky it is. And it will suggest ways to pursue the same or better performance with less risk.

Of course, the computer is no better at predicting the future than humans are, so it doesn’t pay to take its recommendations too literally. It probably would be unwise, for instance, to sell huge chunks of your holdings to buy other investments just to get a small improvement in projected returns and risks, especially considering the commissions and taxes you might get stuck with. But it is worth knowing whether your holdings fit the widely followed guidelines.

If you decide to make changes, hunt for new funds on the site of Morningstar Inc., the Chicago fund-tracking company, at www.morningstar.com. You can do a lot of fund searching for free, but I think the more sophisticated tools offered premium members are worth the price of $11.95 per month. Morningstar also sells an excellent 600-page guide to what it considers the 500 best funds. The new version will be out by mid-February and can be ordered for $35 on the site or by calling (866) 442-1121.