(MONEY Magazine) – New York Senator Daniel Moynihan's proposal to cut Social Security taxes provides an unpleasant reminder of the enormous bite that they take out of your paycheck: up to $3,924.45 this year if you earn $51,300 or more. You can't avoid the tax, but you can ease the pain by making sure to get credit for every penny you earn, so that you are not shortchanged when you start collecting benefits. Indeed, you should check your earnings record whether or not you have reason to believe there's a problem. The General Accounting Office estimates that nearly 10 million workers -- about one in 13 of those who routinely pay Social Security taxes -- have not had all their earnings credited to their accounts. On average, according to the GAO, the mistakes cost workers $204 a year in lost retirement benefits. But the actual amount can be much higher, depending on the size of the mistake. Let's say that you worked from 1955 until you retired this year at age 65 -- with a five-year break in your career from 1961 to 1965. You would be entitled to a monthly benefit of $964, provided you had always paid the maximum Social Security tax. But if your record omits your earnings for just two years -- for example, 1979 and 1985 -- your benefit would drop to $931, a loss of $396 for the year. Over the 17 years that the average person who retires at 65 collects benefits, that would add up to a hefty $6,732 in 1990 dollars. The most common foul-ups result from incorrect reporting by your employer, unreported name changes because of marriage or clerical miscues at the Social Security Administration. ''You must be the final check on the accuracy of your Social Security earnings record,'' says Bruce Schobel, a former high-ranking Social Security official and now a principal at William M. Mercer, a benefits consulting firm in Louisville, Ky. Since Congress last year virtually eliminated the three-year statute of limitations on errors, you can now correct mistakes even if the Social Security Administration previously refused to fix them. Also, if you are already retired and collecting benefits, you can amend your earnings record and usually have your benefits adjusted. Call Social Security at 800-234-5772 and ask for Form SSA-7004, the Request for Earnings and Benefit Estimate Statement. Within six weeks of returning the self-addressed form, you'll receive a breakdown of the earnings that Social Security has recorded under your name for your entire working life. Use your old W-2 forms, tax returns or pay stubs -- and your recollections -- to check Social Security's figures. If you think there's a discrepancy, call the number provided on your benefit statement. Most likely, you'll be asked to send your documents to Social Security; W-2s are the best proof. If you're nervous about parting with originals, you can have officials at the local Social Security office make certified photocopies. If you haven't kept records, try to get copies of your W-2s from the employer you had at the time the error was made. As an alternative, you can get a certified copy of any tax return from the past six years for $4.25 by sending Form 4506 to the Internal Revenue Service Center where you filed. In your vigilance over your future benefits, don't neglect to keep track of what you're paying today. Case in point: Say you, like an estimated 35 million other Americans, work at more than one job. If your total earnings this year exceed $51,300, you are probably paying too much tax. The same may be true if you change jobs during the year. To get a refund or a credit against your income tax for the amount, complete line 60 on your 1040 tax return. If you overpaid in previous years, you can recover the excess by filing an amended return -- Form 1040X -- for the year in question (there is a three-year limit on amending returns). A less common form of overtaxation comes when your employer simply withholds too much Social Security tax. When that happens, the IRS returns the money to your employer, so you must ask your company for the refund.