In the budget for 2021, the government of Canada announced postdoctoral fellowship income will be included in “earned income” which will translate into more RRSP contribution room. This includes income earned during 2021 and beyond. Income earned between 2011-2020 may also be claimed if requested in writing.
CRA publishes prescribed interest rates each quarter. If you are in arrears to the government, for example, late in paying your income tax instalment, you will be charged interest.