My selfemployed business has lost money in2018.do i have to claim this on my2018taxes?can i carry someback to previous years choosing the amounts to claim in each year?

When your self-employed expenses exceed the income earned in the year, you will incur a "Non-Capital Loss". You are able to "carryback" this loss to any of the three previous tax years (if you had taxable income) or carry the amount forward.

You must first report the loss on the current year return, then you can access the screen to request a carryback in one of the following ways:

1. Click on the "Find" icon (little magnifying glass), type in Losses and click Go. On the page titled Your Losses Profile for 2018, check the box Request for Loss Carryback, and continue to the Non-Capital Loss Carrybacks. Here you will see how much of a Non-Capital Loss you have available and you can enter the chosen amounts in the available boxes.
2. In the Review section of TurboTax Online, under Tax Savings Opportunities, you should see a box that says: Any losses not applied to the three preceding years can be carried forward and applied against future years. Click "Explore" and "Applies to me" to be taken to that same screen.
3. In the sidebar of TurboTax, click on Deductions > Losses Profile > Request for Loss Carrybacks.