Year-end tax planning has a branding problem. The name tells you it happens at year-end, so it lands on the December to-do list somewhere between the grocery run and the family dinner.

But several of the moves that actually lower a retiree's tax bill cannot be done on December 31. They need trades to settle, forms to line up, and income decisions to be locked in while there is still runway to change them. By the time the last week of December arrives, the window on some of these has already closed.

September and October are when the real work starts. Here is what needs a head start, with the 2026 mechanics that matter.

Capital-loss harvesting: the trade has to settle, not just execute

Selling a losing position to offset realized capital gains is one of the cleaner year-end moves available. The trap is in the timing.

Stock trades in Canada and the U.S. settle one business day after you place them (T+1). For a loss to count against your 2026 gains, the settlement has to land inside 2026, not the trade. With December 31 falling on a Thursday in 2026, working backward means the practical last trade date is on or about December 30. Cut it any closer and the loss rolls into 2027.

There is a second rule that punishes rushing. The superficial-loss rule disallows the loss if you (or an affiliated person, including your spouse or a corporation you control) buy back the identical security within 30 days before or 30 days after the sale. If you want to stay invested, you need a plan for those 60 days, and that plan takes more than an afternoon to build in late December.

Starting in September gives you time to identify the positions, model the offset against your gains, and stage the repurchase without stepping on the superficial-loss window.

RRIF withdrawals: the withholding gap that surprises people in April

Here is one that is genuinely under-discussed. There is no tax withheld at source on your Registered Retirement Income Fund (RRIF) minimum withdrawal. None.

Withholding only kicks in on amounts above the minimum (10%, 20%, or 30% federally, depending on how far above you go). So a retiree who draws exactly the minimum all year can receive that income with zero tax taken off, then meet a balance owing at filing that they never saw coming.

Q4 is the window to fix this before it becomes an April problem. You can request additional voluntary withholding on your RRIF, or make an instalment payment to the CRA, so the tax is handled through the year rather than in one lump at filing. That request takes time to process with your financial institution, which is exactly why it belongs on the September list, not the December one.

Pension income splitting: decided in Q4, elected at filing

Pension income splitting lets a higher-income spouse move up to 50% of eligible pension income to the lower-income spouse, often dropping the household into lower brackets and protecting benefits.

The election is made at filing, on form T1032. That part is next spring's job. But the thing that creates the splittable income, the RRIF withdrawal amounts and timing, is set during the year and frozen the moment the calendar closes. You cannot manufacture eligible pension income in April for a year that already ended.

Two details shape the Q4 decision. For RRIF income to qualify as splittable, the pensioner generally needs to be 65 or older. And reaching 65 also unlocks the federal pension income amount, a non-refundable credit on the first $2,000 of eligible pension income. If one spouse just turned 65, the amount you draw from the RRIF this fall directly affects how much you can split and credit next spring.

RRSP and FHSA: same season, very different deadlines

People lump these together and get burned on one of them.

Registered Retirement Savings Plan (RRSP) contributions for the 2026 tax year can be made right up to March 1, 2027. That deadline is genuinely in the new year, so there is no rush to write the cheque. But the amount is worth deciding now, because it interacts with everything else on this list: your realized gains, your RRIF income, your target net income for the year.

The First Home Savings Account (FHSA) is the opposite. It follows the calendar year, so 2026 room has to be used by December 31, 2026. Unused room carries forward within limits, but the contribution deadline is a hard year-end line, not a March one. If a contribution is in your plan, treat it as a Q4 deadline.

The thread that ties it all together: your net income and OAS

Every move above changes one number: your net income for the year. And net income is the number Old Age Security (OAS) is measured against.

For the 2026 income year, OAS is recovered at 15% of net income above $95,323. (If you are looking at the current payment period, July 2026 through June 2027, that recovery runs on your 2025 income against a threshold of $93,454. Same 15% rate, different income year. State which one you mean, because mixing them up leads to bad decisions.)

This is why the pieces cannot be planned in isolation. Harvesting a capital loss lowers net income. A larger RRIF draw raises it. Splitting pension income to a spouse can pull the higher earner back under the line. Getting all of that to land in the right place takes weeks of modelling, not a December guess. And as I have written before, losing some OAS is not automatically a bad outcome. It often signals a strong income year. The point is to make the trade-off on purpose. Here is the fuller case on why OAS clawback is not always the villain it is made out to be.

The Q4 head-start checklist

The same idea runs through all of it: the deadline you see is not the deadline that matters.

Where Optiml fits

The hard part of Q4 is not any single move. It is that they all push on the same net income number, and you cannot eyeball the combined effect.

Every Optiml plan determines the optimal decumulation sequence to minimize your lifetime taxes, so the RRIF draw, the loss harvest, and the split are modelled together rather than one at a time. With Compare Plans you can run this year two ways, one where you draw a little extra from the RRIF and split it, one where you harvest losses to stay under the OAS threshold, and see the after-tax result of each side by side before you commit. Your Success Score then shows whether the version you choose holds up, stress-tested against 50 market scenarios drawn from 50,000+ generated return paths. And if you want to sanity-check a specific number, EVA, our AI assistant, is there to explain what a given move does to your plan.

More than 200,000 retirement plans have been run through Optiml. The ones that get Q4 right tend to have one thing in common: they started before the numbers were locked.

The Bottom Line

The December calendar is a decoy. The trades have to settle, the withholding has to process, and the income that gets split has to be earned inside the year. Every one of those needs weeks, not days.

Good year-end planning is not about the last week of December. It is about the first week of September.