It takes years before the IRS will move to seize your accounts or garnish your wages. But interest and penalties are 1%-5% per month, so it adds up fast. And the penalty for filing late is much higher than the penalty for paying late, so file as soon as you can (if you haven't filed already). Pay as much as you can now, then pay more when you can. The IRS will bill you for the penalties and interest.
You can request a payment plan, but the application fee is non-refundable, so it's not worth it unless it will take you more than 4 months to pay your taxes and your taxes owed will be more than about $1000. Getting on a payment plan saves you the penalty but not the interest.
