Your return is done -- that’s how you know the magnitude of your debt. Send it in. Don’t hold it just because you owe money that you can’t pay. But don’t mail it until it’s due, on April 15. (Because April 15 falls on a Sunday, you get a day’s reprieve to Monday, April 16.) You can’t go to jail because you don’t have the money to pay your tax bill, but you can go to jail for not filing. It’s a criminal act, and you’re not a criminal, so get that return in the mail.

If you file and don’t pay in full, the IRS computers will automatically send you a letter asking for the tax due and any interest from the due date.

There is a penalty for late filing of 5% of the tax not paid by the due date for each month, or part of a month, that your return is late. Generally, the maximum penalty is 25%. But if your return is more than 60 days late, the minimum penalty is $100 or the balance of the tax due on your return, whichever is smaller.

Begging and borrowing
But avoiding the late-filing penalty doesn’t get the tax paid. Consider all of the possible sources of money. Can you borrow from friends or relatives? Do you have any equity in your house? If so, a home-equity loan might help eliminate or minimize your tax liability. Moreover, the interest on the loan likely would be deductible on next year’s return.

Do you have potential cash in your credit cards? The interest wouldn’t be deductible, and probably would be much higher than the rate the IRS would charge. Still, you might prefer to eliminate the specter of the IRS, and the post-midnight nightmares that go with it.

But what if you decide to negotiate directly with the government? Understand that the government ranks at the top of the list of creditors who must get paid. Any assets (other than your home or selling your business) are potentially fair game if you owe taxes. Don’t try to hide your assets. That comes under the heading of fraud and you can go to jail for that.

If you can’t come up with the money
What if you can’t find the cash? Remember, you’re not alone.

Ask for an installment plan. In fact, the IRS Web site has an interactive calculator that helps you figure the monthly payment amount and actually prints out an installment agreement for you to file.

If you qualify for a “streamlined” agreement -- generally, if you don't owe more than $25,000 and will be able to pay it off within five years -- you can find out about how long the payments will last. The true length of your payments is a function of both how much you owe and the interest rate charged; since that rate changes every three months, these figures are estimates, not guaranteed maximum payments. If the interest rate goes down, you may actually pay over a shorter period of time.

The rate is calculated on the basis of the short-term federal rate plus 3 percentage points, as of the first month of each quarter. The IRS also charges 9% interest on underpayment (except for large corporate underpayments, which have an 11% rate).

If you don’t meet the criteria for a “streamlined” agreement, you can compare your monthly expenses to the amounts allowed under the IRS’ Collection Financial Standards to determine an appropriate tax-payment amount.

You can actually print out Form 9465, Installment Agreement Request, from the Web site and mail it to the IRS for review and approval. The Web site doesn’t store or transmit any personal data.

If the IRS approves your request, you will be charged a $43 fee. Don’t submit the fee with the form. The IRS normally will deduct the fee from your first monthly payment.

Even if your Form 9465 request is approved, you still will be charged interest and may be assessed a late-payment penalty on any tax not paid by its due date. To limit interest and penalty charges, file your return on time and pay as much of the tax as you can.

Form 9465 is easy to complete. It asks for your name, address, Social Security number, the name of your bank and your employer. (Relax. Based on your W-2 and the 1099 the bank sends, the IRS already has that information.) It then asks how much you owe and how much you want to pay each month. You don’t need an attorney or an accountant to fill it out. If you can pay the outstanding liability within 12 months and promise to keep current with this year’s taxes, almost all requests are granted.

If you can’t pay what you owe within 12 months, request an installment plan that you can realistically meet. The IRS takes a harder line on longer payment periods, but the government has granted such requests after investigating the individual circumstances.