• Make sure you’ve actually filed a 2008 income tax extension: many taxpayers end up owing extra fees because they didn’t complete their 2008 tax extension form filing.

• Make sure you’re aware of the penalties: even if you filed a 2008 tax extension, you’re still going to owe money when you pay late. Fortunately, the penalties for paying late are much lower than the penalties for filing late. You’ll owe .5% of your total bill for each month you’re late. You’ll also have to pay 5% per year in interest—steep, but much lower than the 5% per month you could owe if you file late, too.

• Don’t forget about state taxes: If you’ve filed your federal tax extension form, but not your California income tax extension, you could be on the hook for fines from the state. If you’re in the military, tax extensions can get even more complicated, because you may serve in different states—but it’s fairly simple to sort out, since the paperwork is all available.

• Gather your tax forms: you don’t want to come up short when it’s time to actually complete the filing. If you’re unable to get the forms, make some plans in advance: you’ll have to estimate your income and withholdings, and the IRS may end up questioning the estimates. It can get fairly complicated, so it’s best to avoid the trouble and track down your forms.

• Double- and triple-check your work: the IRS is always picky about errors—but if you filed a 2008 tax extension, they’re going to pay extra attention. You might know how long the tax extension does last, but you don’t know how long those errors will stick around. This isn’t because they want to pick on late filers, or even because people who file late make more errors. The reason is simple: they’re less busy when it’s not tax season, so they have more time to carefully examine your return. So spend some extra time reading over your 1040; extension filing won’t help you there.

The good news? Although it used to be difficult, filing after the deadline once you file a 2008 tax extension form has never been easier. You can efile (an electronic file extension) online, and have your credits automatically calculated. It’s faster and simpler than a traditional return, and could help you get even more money back! And even if you expect to owe money, you don’t have to pay until you’ve completed the filing (so you can wait until you know how much you’re saving—it amounts to getting to file for free!)