Why do CPP, CPP2, and EI even stop being deducted partway through the year?
Because all three are calculated against an annual ceiling, not an ongoing percentage of every dollar you ever earn. CPP applies 5.95% to pensionable earnings between the $3,500 basic exemption and the $74,600 Year's Maximum Pensionable Earnings (YMPE) for 2026, capping annual base CPP at $4,230.45. CPP2 adds a further 4% on earnings between the YMPE and the higher $85,000 Year's Additional Maximum Pensionable Earnings (YAMPE), capping at $416. EI charges 1.63% up to the $68,900 Maximum Insurable Earnings (MIE), capping at $1,123.07. Once your year-to-date earnings push the relevant contribution to its cap, your employer legally must stop deducting that specific amount for the rest of the calendar year, then start fresh at $0 again on 1 January.