If you’ve done your tax return and realize you owe but can’t pay, the worst thing to do is nothing.

You may be fearful of what lies ahead, but eventually the IRS will track you down, and by then the penalties and late fees will make your debt that much larger.

In fact, the interest on unpaid tax debts is compounded daily and is charged from the due date of the return until the date of payment. The interest rate the IRS charges is the Federal Reserve’s benchmark short-term rate plus 3 percent, which these days means 8.25 percent.

Although the IRS doesn’t have the storm-trooper reputation it once did, the agency hasn’t gone SpongeBob-SquarePants-soft. They won’t giggle and forgive your transgression like the sweet sea creature in the Nickelodeon cartoon. They will come after you hard.

If nothing else, at least file your tax return even if you can’t pay the full or even a partial amount. That’s because the total penalty for failure to file and pay can be 47.5 percent. Filing your return would at least save you the 22.5 percent portion of the penalty.

This time of year, companies prey on individuals who either have not filed and owe, or have filed and can’t pay. These firms make promises that they can get the IRS to settle your tax debt for a fraction of what you owe.

In the majority of the cases, this is just a deception. Essentially what these promoters do is have you apply for what’s called an offer in compromise, or OIC. This allows the IRS, under certain circumstances, to accept less than the full tax payment.

An OIC is tough to get. Last year the IRS received 59,000 requests for offers in compromise, but only 15,000 were granted.

You have to be experiencing some unusual economic hardship to qualify for an offer in compromise. The IRS will not accept an OIC unless the amount you offer to pay in lieu of your full tax obligation is equal to or greater than what the agency thinks it can reasonably collect from you.

That means you are expected to exhaust all ways to pay your tax bill, including liquidating any assets and bank accounts. In addition, the IRS will look at your present and future income, allowing certain amounts for basic living expenses. And among other things, you have to provide detailed information to prove that you are practically destitute. You also have to pursue all other payment options, such as an agreement that allows you to pay your obligation in monthly payments.

Instead of contacting one of those promoters promising to get you an offer cutting your tax bill to pennies on the dollar, go through the checklist in IRS Form 656 “Offer in Compromise” to determine if you are eligible. This form has all the instructions for submitting an offer. There’s also a worksheet – you can fill it in online at www.irs.gov – which is not too complicated and can help you determine how much you would be expected to offer. Look for the OIC “fill-in format.”

Last year there were some major changes to the OIC program. For example, to be granted an OIC in many cases, you have to make a 20 percent, nonrefundable, upfront payment along with your OIC offer. If you’ve completed your return and you find you can’t pay your tax debt, call (800) 829-1040. If you are a small business owner, call (800) 829-4933.

If you cannot pay the full amount due as shown on your return, ask to make monthly installment payments. You’ll have to pay a one-time fee of $105. In 2006, 2.7 million taxpayers paid their tax bills in monthly payments, according to the IRS. To request an installment agreement, use IRS Form 9465 “Installment Agreement Request” with your return. For more details on installment payments, refer to IRS Tax Topic 202 – “Tax Payment Options,” or Publication 594, “What You Should Know About the IRS Collection Process.”

I urge you, if you owe back taxes, not to let your fear or lack of funds paralyze you into doing nothing.