Some people receive income from many different sources once they retire. These sources can include CPP, OAS and other pensions. These pensions are usually in the dark about any other income you may have coming in, and as such, they do not take that income into account when deducting tax. If you have a general idea of how much total income you receive, contact CPP, OAS, and your pension to be sure they are deducting the appropriate amount of tax to avoid payments when you have your taxes prepared.