Note to self: Plan my retirement. But first I need to pay that parking ticket, and make a vet appointment for the dog and, and, and ...

Sound familiar? There are plenty of ways to ruin your retirement. (If you're stumped, here are nine.) Don't let a niggling "to do" list come between you and the carefree, romping lifestyle you want for your future. In fact, just put the grocery list down for five minutes and see where you stand.

What can you do in just 300 seconds? This Ballpark Estimate worksheet will help you do some back-of-the-envelope retirement accounting and take a lot of the guesswork out of saving for your future. That's a lot more future-casting than most people have done at your tender age.

This brief but eye-opening exercise, provided by the American Savings Education Council, asks you to ponder the big questions about your golden years. (But just for a moment, honest.) For instance, how much of your current annual income will you need? For low-key retirees, 70% to 80% of your salary may do quite nicely. For those many years from retirement, with visions of a long, active life ahead, 100% to 120% of your current income may be necessary. The good news is that many expenses decline or disappear completely in retirement.

You'll also be asked to consider any money you'll get from Social Security, an employer's pension (for the lucky few out there), or earnings from part-time work. You may think you want to quit the 9-to-5 world for good, but not everyone wants to be -- or can afford to be -- a beach-bum grandparent. Consider a "rehearsal retirement" to make sure you'll actually like the life of leisure you've planned. It's also a great excuse to take a long weekend or two and call it "research."

The interactive worksheet will estimate how much money you need to bank in today's dollars for each year you'll be retired. You'll then see the total amount of money you should have in your brokerage account on the day you retire. Once you provide your current savings and the years you have until retirement, a number that's still mind-numbingly large (but less so) will appear.

Postpone your panic attack. (This instruction is actually in the official Ballpark Estimate worksheet directions.) The accounting whizzes working behind the scenes provide a much more reasonable yearlysavings goal, which should bring the color back to your face. (Tonight you'll give thanks for the magic of compound interest and vow to improve your investing smarts with other soon-to-be retirees.)

Once you've tabulated the results, you may feel a wee bit more generous toward your future self. How about upping the contribution to your work retirement plan and adding to your IRA? Even a few percentage points can make a big difference in the long term.

Now rerun your Ballpark Estimate calculations. See? You're already making progress.

For other moves you should make for your golden years -- insurance, housing, asset allocation, and other post-9-to-5 surprises, grab a free issue of Rule Your Retirement.

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Dayana Yochim is very good to her future self, but she is also very good to her present self. The Fool has an ironclad disclosure policy.