Affluent clients facing a big tax bill often have one of two reactions, according to CPA and financial planner Jerry Love: They either try to avoid filing or they want to negotiate a deal.

Neither is a good strategy, he says. Failing to file a tax return triggers much bigger penalties than failing to pay (5 percent versus 0.5 percent per month). And despite television ads to the contrary, settlements aren't easy to win, particularly when you have assets the IRS can go after.

Haggling "might work with a vendor," says Love of Abilene, Texas. "It's not going to work with the IRS." Unpaid tax bills can lead to tax liens on property, trashed credit, seized bank accounts and, though rarely, even jail.

The consequences of owing the IRS are severe enough that people should search hard for ways to pay. That may include borrowing money from friends or family, drawing money from a home equity line of credit or selling investments held outside retirement accounts. Sometimes clients who say they can't pay actually have the means, just not the cash, says CPA Jonathan Gassman of New York City.

"Find the liquidity you need by calling your broker and selling some stocks," Gassman says. Before pulling out a credit card, though, taxpayers should calculate the costs versus the IRS options. For those who can pay quickly, just not right away, the tax agency offers an extra 120 days to pay without a formal installment agreement.

During those 120 days, taxpayers will owe penalties of 0.5 percent per month on the unpaid balance plus interest, currently at a rate of about 3 percent. Installment agreements lower the penalty rate to 0.25 percent a month and cost $120 to set up (or $52 with automatic withdrawals from a bank account). All in, installment plans typically cost 8 percent to 10 percent a year and can extend for six years, Love says.

Using a credit card, meanwhile, triggers an upfront charge of about 2 percent and balances accrue at the card's rate, typically 15 percent or more. Some credit cards offer lower teaser rates for purchases, although those deals generally expire after 14 to 21 months.

Many people erroneously think they can get extra time to pay by filing an extension, but that's not how extensions work, says Lisa Greene-Lewis, a CPA and tax expert for TurboTax. Taxpayers are expected to estimate and pay what they owe by April 15, even when they request six more months to file the actual return.

Those who can't pay should still file returns on time to dodge the failure-to-file penalty and start the clock that typically limits IRS audits to three years from the filing or due date, whichever is later, Gassman says.

"You always want to get the statute of limitations running," he says. Those who owe $50,000 or less in taxes, penalties and interest can file online for an installment agreement. Those who owe more than $50,000 are subjected to more paperwork and scrutiny.