So you haven't filed your 2009 income tax return.

And the midnight April 30 deadline has come and gone, which means you may face a penalty. Now what?

Filing your return as soon as possible will prevent you from being charged additional interest and penalties. Waiting for the Canada Revenue Agency (CRA) to catch on is not a good idea. While it can sometimes take years for the CRA to send out a request for a missed tax return, interest begins accruing on May 1.

If, however, you expect to receive a tax refund, take a deep breath, because you're off the hook. There is no penalty for filing late unless you owe the government money (though certain government benefit cheques may be delayed). Generally, unless you owe, there is a three-year grace period for filing a return.

Now the bad news. When Canadians miss the payment deadline, the CRA automatically charges a penalty to their outstanding balance. Additional penalties and interest continue to build up until the return has been filed and the total balance has been paid.

Penalties for overdue tax returns include:

The CRA may forgive penalties and interest in special circumstances. These include:

Taxpayer relief requests may be made to any CRA office. A copy of the taxpayer relief request form, titled "form RC4288, Request for Taxpayer relief," may be downloaded from the CRA website (www.cra.gc.ca/forms) or ordered by phone ( 1-800-959-2221 1-800-959-2221).

Another common tax issue this time of year is the realization that something was forgotten in an already-filed return.

If this is the case, don't fret. The CRA doesn't frown too harshly on incomplete tax returns as long as it was an honest mistake.

If you have found something that you forgot to include in your return, do not file another return. Wait for your notice of assessment before contacting the CRA to request a change in your tax return.

There are two ways to request a change to your completed tax return: online or through regular mail.

Online, log into your account on the CRA website and select the "Change my return" option. From the website, you can update tax returns from 2009, as well as your tax returns from the previous two years.

By regular mail, send in a "T1-ADJ T1 Adjustment Request" form. You also have the option of mailing the CRA a letter containing your social insurance number, a daytime phone number, your address, your signature and the supporting documents for the changes you would like to make.

Tax returns may only be updated for the 10 years before you request the update. Therefore, a request to update a 1999 tax return cannot be sent in 2010.