You waited too long.

It’s April 15 and you’re sweating out your tax return, looking for those documents you received in January and February and trying to avoid paying too much.

First, don’t panic, experts say. Everything will be all right.

You’re among the 20 percent who wait until two weeks or less before the deadline to calculate and file your return.

Accountants at four firms say you should consider a time extension to file your 2004 tax returns.

At Smith Barta, accountants say it’s better to extend until you can file a complete return than to amend to include inadvertently omitted items. Cohen & Co. reminds you that the extension pushes back only the time to file, not the date on which tax payments are due.

But you should pay all the tax required by April 15, says Bruner Cox. Taxes paid after the due date could be subject to interest and penalties. When you make the calculation of potential tax, it may be better to overestimate the items you are unsure of since you can request that any overpayment be refunded.

Use Internal Revenue Service Form 4868 to obtain a four-month extension to file your federal return. Another two months can be requested in August if you have a good reason. This gives you until Oct. 15 as the final deadline.

Smith Barta has one more tip for those who plan to rush into an accountant’s office with their tax information — your procrastination does not make a CPA’s crisis. If you use a paid preparer, brace yourself for an extension of time to file the return. You aren’t his only client.

If you’re plunging ahead with your return, ask a family member or friend to help you get your tax information organized and make phone calls to gather missing information.

Tax-preparation software is designed to identify available deductions and credits, and online banking tools gather interest income, mortgage interest and real estate tax data.

Don’t forget to double-check all of your entries before finalizing your return. It will take only a few minutes.

For those waiting until the very last minute, check with your local post office about hours. Some post offices are open until midnight on April 15.

And before you seal that envelope, make sure you sign the form.