How to Apply for OAS and GIS by Mail (Form ISP3550) in 2026

• OAS does not always start by itself. If Service Canada has enough information about you, you are enrolled automatically and get a letter around your 64th birthday. If you do not get one, you likely have to apply.
• One form covers both benefits. Form ISP3550 is the application for the Old Age Security pension and the Guaranteed Income Supplement.
• The GIS is income-tested and non-taxable. It is a monthly top-up for low-income OAS recipients, and it is the benefit people most often fail to claim.
• The GIS renews on your tax return. File your income taxes every year and your GIS is reassessed automatically each July. Miss the filing and it can stop.
• OAS starts at 65, or you can wait. Defer up to age 70 and your monthly amount goes up 0.6% for every month you wait.
• You can do the whole thing by mail. A dated copy of the form plus a PostPal mailing confirmation is your record, and you never visit a post office.

This is the first thing to settle, because everything else depends on it.

If Service Canada already has enough information on file about you, it enrols you in Old Age Security automatically. You will get a letter the month after you turn 64 telling you so. If that letter shows up and the details are right, you do nothing. Your pension starts at 65.

But automatic enrolment is not guaranteed. Plenty of people fall outside it, often because their record is incomplete or they have spent years outside the country. The way to tell is simple: if it has been a month past your 64th birthday and no enrolment letter has arrived, assume you have to apply, and contact Service Canada or get the form started.

Do not wait around hoping it sorts itself out. That is how people end up applying at 66 and losing months of payments they were owed.

The official rundown of who is enrolled automatically and who must apply is on the Old Age Security apply page at canada.ca.

There are two ways to apply when you have to apply.

The first is online, through your My Service Canada Account. If you already have an account and your situation is straightforward, this is the quick route. Be aware you may still be asked to mail in supporting documents afterward.

The second is the paper form, ISP3550. It is the application for the Old Age Security pension and the Guaranteed Income Supplement, both on one form. A separate reference guide walks you through filling it in. The paper route is the right call if you do not use online accounts, if you are helping a parent who would rather sign a piece of paper, or if your situation has wrinkles that the online flow does not handle cleanly.

Print the form, fill it in, and send it. You do not need a printer at home or a trip to a Service Canada office to get it in the mail.

Here is the one most people get wrong.

The Guaranteed Income Supplement is a monthly payment on top of OAS for low-income seniors. It is non-taxable, and it can be a meaningful amount of money. The catch is that not everyone gets signed up for it automatically the way they might for OAS, and a lot of people who qualify never claim it simply because they did not know to.

If you are applying for OAS on the paper ISP3550, the GIS is right there on the same form. Fill in that section. Do not skip it because you assume your income is too high or because the wording looks like it does not apply to you. Let Service Canada make that call.

How much you might get depends on your income and your marital situation, so we are not going to invent a number here. Use the benefits estimator at canada.ca to get a figure for your own case.

The overview of who qualifies is on the Guaranteed Income Supplement page.

The GIS is reassessed every year in July, based on your income from the previous year. That income comes from your tax return.

So the renewal is automatic, but only if you file. File your income tax return on time each year and Service Canada reassesses your GIS without you lifting a finger. Skip the filing, file late, and your GIS can be reduced or stopped until you sort it out.

This trips up a surprising number of seniors, especially people with little or no income who assume they do not need to file because they owe nothing. For the GIS, filing is the renewal. No return, no reassessment.

If you genuinely cannot file a return, you can give your income information to Service Canada directly instead, by mail or in person. But for almost everyone, the simplest path is just to file every year, on time. Canada.ca lays this out on the receiving your GIS benefit page.

OAS generally starts at 65. You do not have to take it then.

You can defer your OAS pension for up to five years, to age 70, and your payment grows for every month you wait. The increase is 0.6% per month, which works out to 7.2% per year, up to 36% more if you hold off all the way to 70. That is a permanent bump for the rest of your life, not a one-time bonus.

Whether deferral makes sense for you depends on your health, your other income, and whether you need the money now. If you do plan to start later than 65, note that Service Canada wants to know in writing, generally no later than six months after your 65th birthday. After 70 there is no benefit to waiting, and you can actually lose payments by delaying further.

One thing worth knowing: the GIS is for people who are already receiving OAS. If you defer OAS, you are not getting the GIS during the wait. For a low-income senior, that trade-off usually points toward starting OAS at 65 rather than deferring. The full breakdown is on the when to start your OAS pension page.

The paper form goes to a Service Canada processing address, and the right one can depend on where you live.

Rather than print an address here that might be wrong for your case, we keep a directory page up to date with the current mailing details. See where to mail your OAS/GIS application and use the address that matches your situation.

Address the envelope to that, and your form is on its way.

You do not need to stand in line anywhere to send this.

With PostPal, you upload or type your filled-in ISP3550 at /send. We print it, put it in an envelope, and mail it through Canada Post the next business day. It costs about $6 flat. Then we email you a dated mailing confirmation, which tells you exactly when it went out.

For proof, keep two things: a dated copy of the completed form you sent, and that mailing confirmation. Between them you have a clear record of what you submitted and when, which is all you need if a question ever comes up about whether or when you applied.

This is also the easy way to handle it for a parent. Fill in the form, send us the file, and the envelope is in the mail without anyone driving across town.

Am I automatically enrolled in OAS?

Maybe. If Service Canada has enough information about you, it enrols you automatically and sends a letter the month after you turn 64. If a month has passed since your 64th birthday and no letter has arrived, assume you need to apply and contact Service Canada to confirm.

Do I have to apply for the GIS separately?

The GIS is on the same form as OAS, the ISP3550, so if you are applying on paper you handle both at once. The important thing is to actually complete the GIS section. Do not skip it because you assume you earn too much. Let Service Canada decide.

Why did my GIS stop?

The most common reason is a tax return that was not filed or was filed late. The GIS is reassessed each July based on your previous year's income, and that comes from your return. File your taxes every year, on time, and the renewal happens automatically.

What is form ISP3550?

It is the Service Canada application for the Old Age Security pension and the Guaranteed Income Supplement. One form, both benefits. There is also a reference guide that explains how to fill it in.

Can I apply for OAS online instead of by mail?

Yes, through your My Service Canada Account. You may still be asked to mail in supporting documents afterward. If you do not use online accounts, or you are helping someone who prefers paper, the ISP3550 by mail is a clean alternative.

Should I defer my OAS to age 70?

It depends. Deferring raises your monthly amount by 0.6% for each month you wait, up to 36% at 70. But you do not collect OAS or the GIS while you wait, so for low-income seniors who would qualify for the GIS, starting at 65 usually makes more sense. Run your own numbers with the estimator at canada.ca.

Do I need to file taxes if I have no income?

For the GIS, yes. Filing your return is what triggers the annual renewal, even if you owe nothing. No return means no reassessment, and your GIS can stop.

The whole thing comes down to a few moves. Check whether you were enrolled automatically. If not, fill out the ISP3550 and complete the GIS section even if you think you will not qualify. Mail it. Then file your taxes every year so the GIS keeps renewing.

None of it requires a trip to a Service Canada office or a post office. You can apply by mail, keep a dated copy, and get a confirmation of the date it was sent, all from home.

Mail your OAS/GIS application with PostPal →

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