(MONEY Magazine) – We've got two heads-ups for any-one filing an 11th-hour tax return:

--The dependency error. If you intend to claim any dependents on your '96 federal income tax return, make sure you get their names and Social Security numbers exactly right on the 1040. Otherwise, you could be out hundreds of dollars. In an effort to crack down on the millions of taxpayers who invent fake dependents, this tax season the IRS can disallow exemptions for dependents listed incorrectly on tax returns.

In prior years, if you, say, accidentally left your daughter's Social Security number off your 1040, Uncle Sam processed your return and then sent you a request for the proper info. Make the same error now, and the IRS may recalculate your return as though your child doesn't exist, slashing your refund or causing you to owe extra taxes. The cost for a married couple filing jointly in the 31% tax bracket who lose one exemption: $791 ($2,550 exemption times 0.31). To straighten things out, you'll need to file an amended return, Form 1040X. Says Tom Sherman, a tax partner in the Minneapolis office of the accounting firm Coopers & Lybrand: "Be very careful. Otherwise, you risk getting caught in the IRS' paper chase."

Filing electronically may help prevent mistakes. Tax software and tax-filing Websites typically reject any return that doesn't contain complete data, giving you a chance to perfect your return before the IRS rejects it.

--Using a delivery service. Tax filers can now use IRS-approved private delivery companies to send in their returns by April 15 and be sure that their taxes will be considered filed on time. Until this year, unless you used the U.S. Postal Service, the IRS would not guarantee that a return mailed on time was filed on time. Not all carriers will get the IRS' sanction, though. So before you pick a delivery service, make sure it will get the IRS' blessing. Two good bets: Federal Express and United Parcel Service.

--Peter Keating and Beverly Goodman