Is there a simple way of calculating how much you can contribute to an RRSP if you have never contributed at all?
Generally it's about 18% of your lifetime taxable earnings but there is a maximum for each year so this isn't an absolute.
If you do not have a copy of your notice or a T1028, you can find out the amount of your RRSP deduction limit by going to My Account, Quick Access or by calling our automated TIPS RRSP service. For more information, see My Account and Tax Information Phone Service (TIPS).
This link provides how to get it from the gov't or how to calculate it yourself.
You can get your available RRSP Contribution amount from last years notice of assessment or by calling the Canadian Revenue Agency.