Do I pay into both CPP and US Social Security if I work in both countries?

What the totalization agreement does

The Agreement on Social Security between Canada and the United States has been in force since 1984 and solves two problems at once. It prevents dual coverage, where the same paycheque would be charged both CPP and US Social Security tax, and it provides totalization, so that years spent in one country can help you qualify for benefits in the other. It covers the Canada Pension Plan and Old Age Security on the Canadian side, and the US Social Security retirement, disability and survivor programs, together with the Medicare payroll tax, on the American side.

Two things fall outside it. Quebec has its own parallel agreement for the QPP, and Employment Insurance is not a social security program for these purposes, so an EI obligation is decided by ordinary Canadian payroll rules rather than by the agreement. Income tax is a separate question again, governed by the tax treaty; the coverage rules below say nothing about which country taxes your salary.

Which system you pay into: the three coverage rules

The agreement decides coverage with a short set of rules, applied in order:

1. Employees pay where they work. The default rule is territorial. Work performed in Canada is covered by CPP; work performed in the US is covered by US Social Security. An Ontario resident working from home for a US employer is under CPP, and a Canadian commuting daily to a job in Detroit is under US Social Security.
2. Temporary transfers stay home. The detached worker rule lets an employee who is sent by their employer to work in the other country for a period expected to last five years or less remain in the home system. A Toronto employer seconding staff to a US office for three years keeps them on CPP and exempts them from FICA; a US employer sending someone to Canada keeps them on US Social Security and exempts them from CPP.
3. Self-employed people pay where they live. A self-employed person contributes only to the system of their country of residence, wherever the work is physically done. A Brampton consultant flying to New York for client work stays under CPP; a US resident freelancer billing Canadian clients stays under US Social Security and Medicare.

The detached worker rule depends on the transfer being temporary from the outset. An open-ended move, or one that stretches past five years without an agreed extension, falls back to the territorial rule.

The certificate of coverage: how you prove the exemption

An exemption under the agreement is only as good as the paper behind it. The home country issues a certificate of coverage confirming which system applies, and the host-country employer keeps it on file to justify not withholding local contributions.

• For someone staying in CPP while working in the US, the Canadian employer applies to the CRA using Form CPT56; the certificate satisfies the IRS that no Social Security or Medicare tax is due on that employee's wages.
• For someone staying in US Social Security while working in Canada, the US employer requests the certificate from the Social Security Administration's Office of Earnings and International Operations, and the Canadian payroll uses it to skip CPP.
• Self-employed people request their own certificate from the country they live in, to show the other country's authorities if asked.

Apply before the assignment starts. Without a certificate, a US employer will withhold FICA by default, and recovering it afterwards means asking the employer for a refund and, failing that, filing Form 843 with the IRS. The same recovery route applies to Canadians whose US employer withheld FICA on work they performed from Canada, a situation we cover in do Canadians working remotely for a US company pay US tax.

How the agreement helps when it is time to collect

Totalization matters most at retirement. Each country still calculates the benefit only on contributions made to its own system, but it can count periods in the other country to decide whether you qualify:

• US retirement benefits normally need 40 quarters of coverage. With at least 6 US quarters, the SSA can add your CPP contribution years to meet the 40, and then pays a pro-rated benefit based on the US years alone.
• OAS requires 10 years of Canadian residence after 18 to be paid in Canada and 20 years to be paid abroad. Periods of US coverage can be counted toward those residence tests, although the amount is still based on actual Canadian years.
• CPP retirement pension needs only one valid contribution, so totalization mainly helps with CPP disability and survivor benefits, which have minimum contribution requirements.

For years, Canadians collecting both CPP and US Social Security saw their US benefit reduced under the Windfall Elimination Provision. That provision was repealed by legislation signed in January 2025, effective for benefits payable from January 2024, so as at the time of writing a CPP pension no longer reduces a US Social Security benefit. Retirees whose US benefit was cut before the repeal should confirm that the SSA has recalculated it.

How each pension is taxed once you retire is a treaty question rather than a coverage question. We cover both directions in how CPP and OAS are taxed if you retire in the US and how US Social Security is taxed in Canada.

How we handle coverage for cross-border workers and employers

We see the agreement from both ends: the Canadian professional on a TN visa asking why FICA appears on the pay stub, and the Canadian company sending its first employee to a US client site. For workers, we confirm which rule applies, request the certificate where one is available and prepare the refund claims when contributions were taken in error, alongside the Canadian and US returns described in our guide for Canadians working in the US. For employers, we file the CPT56 applications and set up the payroll so the exemption is applied from the first cheque. Both sit within our cross-border tax services.

Source: SSA — Totalization Agreement with Canada; CRA — Form CPT56, Certificate of Coverage under the Canada Pension Plan.