Government form, explained · Canada (Service Canada)
ISP-3550: the combined OAS and GIS application
ISP-3550 covers Old Age Security and the Guaranteed Income Supplement on one form. Before filling it out: you may not need it at all.
You may not need this form
If Service Canada has your eligibility information, you get an enrollment letter around your 64th birthday. This means you are enrolled automatically and do not need to apply. If you are at least 1 month past your 64th birthday and have not received a letter, contact Service Canada to find out if you need to apply.
What the form covers
ISP-3550 is the combined paper application for OAS and GIS. Apply online in My Service Canada Account once you are at least 1 month past your 64th birthday, or apply by mail using this form.
Where to get it
Download the current 10-page form from the Service Canada forms catalogue:
ISP-3550.pdf →ISP-3550A is the reference guide for the application: consult it alongside the form.
Common mistakes
- ✗Filling out ISP-3550 without first checking for the enrollment letter: most people are auto-enrolled and never need it.
- ✗Applying online before you are at least 1 month past your 64th birthday, before the online route becomes available.
- ✗Treating a missing letter as an automatic requirement to apply, rather than contacting Service Canada to confirm.
Common Questions
What is ISP-3550?
ISP-3550 is the combined paper application for Old Age Security (OAS) and the Guaranteed Income Supplement (GIS). It covers both programs on one form.
Do I need to fill out ISP-3550?
You may not need this form. If Service Canada has your eligibility information, you get an enrollment letter around your 64th birthday and are enrolled automatically. If you are at least 1 month past your 64th birthday and have not received a letter, contact Service Canada to find out if you need to apply, rather than assuming you do.
How do I apply if I am not auto-enrolled?
Apply online in My Service Canada Account once you are at least 1 month past your 64th birthday, or apply by mail using ISP-3550.
Is there a guide to filling out ISP-3550?
ISP-3550A is the reference guide for the application.
Turning 65?
The full guide covers CPP, OAS, GIS, and the Allowances together, plus a free personalized checklist.
Guidepost is not a law firm. This is general information, not financial or legal advice, verify current requirements with Service Canada. Full disclaimer.