The better you understand the tax rules, the less likely you are to make mistakes when you file. For example, if you don't claim correct deductions, the Canada Revenue Agency will adjust your return. Here are some common areas where people slip up:

• Union and professional dues Your employer may withhold dues from your pay. If they do, they will note this on your T4 slip as a taxable benefit and you can claim a corresponding deduction. You may also get a receipt for these dues from your union or association. But you can only claim the deduction once.
• Moving expenses If you were reimbursed by your employer for some or all of your moving expenses, you must include this as income on your tax return. You can only claim moving expenses that were not reimbursed. Learn more now
• Other deductions (line 232 on your tax return) Some people use this line to claim personal or living expenses that are not legitimate tax deductions. Examples of disallowed deductions include: funeral costs, wedding costs and legal fees paid for separation or divorce agreements.
• Public transit costs You cannot claim day passes, tokens or tickets. You can only claim a monthly or annual transit pass. If your employer has paid for your public transit pass, and included it as a taxable benefit in your employment income (check your T4), you can still claim the credit. Learn more now

For a list of tips to reduce the number of adjustments to your return, learn more now from the CRA.

What if I need to change something later, after I have filed?

If you find an error or you need to change something and your return has not yet been processed, do not refile your return. Wait until you receive your notice of assessment before you request the change. You can only go back 10 years to request a change.

To request a change or adjustment:

1. Complete the T1 Adjustment Request. Or you can make online changes to your most recent return, or to returns from the past two years through CRA's electronic service. Online changes are sent directly to CRA processing systems.
2. Send in any documents to support the changes you want to make to the CRA. It takes the CRA about eight weeks to process the request.
3. Once the CRA has completed their review, they will send you a notice of reassessment showing any changes to your return. If they did not accept the changes, they will provide a letter of explanation.

Remember: If you prepare your own tax return, be sure to check it carefully. It will save you problems later on. If you are worried about making mistakes, you may want to get help from a tax professional. Content in this section is provided in partnership with the Investor Education Fund, a non-profit organization promoting financial literacy to Canadians. To find out more go to GetSmarterAboutMoney.ca.