I am at the point where it's asking me for details from my common law spouse's federal tax return. But she hasn't completed hers yet. How do I proceed?

You can put an estimate of her income as per her T4 information slip and if it is above  $14,398 for 2022 it will not matter as you would not be eligible to claim the spousal amount. The importance lies with not claiming the spousal amount if you are not eligible as the Canada Revenue Agency may require repayment of such.

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