If you think you owe:

You should have your taxes reviewed and make sure you aren't missing anything. Then, particularly if you haven't filed an extension, you should file sooner rather than later, even if you can't pay right away.

You want to file, because the IRS assesses two penalties; a failure to file and a failure to pay. The failure to file is 5 percent of the taxes due (assessed each month, but not exceeding 25 percent). If you file more than 60 days late the minimum late filing penalty is the lesser of $100 or the amount due. The failure to pay penalty is .5 percent of the taxes due 10 times less- (again assessed each month, and not exceeding 25 percent).

The total penalties assessed if both apply can be 47.5 percent.

In some cases, penalties may be waived. There are statutory exemptions to late filing penalties, such as being in a combat zone. There are reasonable cause exemptions, such as illness or natural disaster. Reasonable cause exemptions are evaluated by the IRS on a case-by-case basis. If you have generally paid and filed in a timely manner in past years, you may be eligible for a first time penalty abatement. On 2014 taxes, there is penalty relief for the repayment of excess advance payments of the premium tax credit.

In addition to penalties, interest charges are assessed on late payments. The interest charge is the short term rate plus 3 percent. Interest charges are rarely waived.

If you expect a refund:

You have three years from the filing due date to file for a refund. You are not penalized for filing late.

It's a good idea to calculate your taxes though, and confirm you are due a refund. Otherwise, penalties may be accruing.

In either case, there are advantages to filing sooner rather than later:

a. some options for reducing your taxable income, such as contributions to IRAs or HSAs, aren't available after April 15.

b. paperwork associated with the return can get lost or misplaced.

c. installment plans to pay your taxes and offers in compromise require all prior year returns be filed.

d. future refunds may be delayed until prior year returns are filed.

e.If you don't file a return, the IRS may file a substitute return for you, which may not give you credit for all deductions and exemptions for which you are eligible. If this happens you will be sent a Notice of Deficiency, and given just a short window of 90 days to respond.

Don't lose out on a refund, and don't let a small tax bill become a large one.