When your bonus gets shredded by withholding

A bonus lands, you check the deposit, and a third of it is gone. Or worse: the withholding looks fine all year and then you owe five figures at filing. Both are the same underlying problem — payroll withholding is a rough estimate, not your tax bill.

The one distinction that explains everything

Tax withheld at source is a prepayment, not a settlement.

Payroll guesses, in real time, what to remit to the CRA on each cheque. Your actual tax depends on the entire year’s picture: salary, bonus, RSU vests, deductions, province, and any other income. The two only reconcile when you file. So there are really three different problems hiding behind “why is my withholding so high”:

1. Over-withheld — you’ll get it back as a refund. Annoying, not harmful.
2. Under-withheld — a tax bill (and possibly instalment interest) is coming.
3. Cash-flow mismatch — the annual number is fine, but the timing stings.

Diagnose which one you have before trying to “fix” payroll. They have completely different fixes.

Why bonuses look over-taxed

Employers usually apply supplemental withholding to bonuses — they annualize the lump sum as if you earned it every pay period, which pushes the estimate into a high bracket. If your real marginal rate is lower, you’ve simply over-prepaid and the refund follows.

Why RSU vests often go the other way

The RSU under-withholding gap

At vest, your employer typically does a sell-to-cover — selling some shares to remit tax. But the rate withheld is often below your true marginal rate, which in the top bracket runs ~48–54% combined depending on province. If you under-withhold on a large vest, the shortfall lands at filing. Plan for it, and don’t spend the proceeds assuming the tax is already handled.

Where T1213 actually fits

CRA’s T1213 Request to Reduce Tax Deductions at Source lets you authorize payroll to withhold less during the year — but only when you have deductions or credits that payroll can’t see, such as:

• large RRSP contributions made directly (not through payroll)
• deductible support payments
• significant charitable donations
• carrying charges or rental losses

It’s the right tool when you’re chronically over-withheld because of real, ongoing deductions — it gets your own money back monthly instead of waiting for a refund. It’s the wrong tool if your problem is under-withholding, or if the expected reduction is small. Approval takes weeks, so file early in the year.

What not to do

• Don’t read a low withholding rate as a low tax rate. It’s the most expensive misread in this whole topic.
• Don’t spend variable comp on arrival. Treat bonus and RSU proceeds as uncommitted until the full-year tax picture is modeled.
• Don’t file a T1213 reflexively just because you got a big bonus — it only helps if you have deductions payroll isn’t already capturing.

Common planning moves

• Make RRSP contributions in high-income years to deliberately reduce tax on bonus/vest income.
• Model the after-tax value of an RSU vest before treating it as spendable.
• If you under-withhold every year, set up quarterly instalments or park a reserve so the bill is never a surprise.

Checklist

• Separate withholding from final tax owed — they’re not the same.
• Figure out whether you’re over-withheld, under-withheld, or just mis-timed.
• Model bonuses and RSUs against your full-year income, not payroll intuition.
• Keep large variable-comp dollars parked until the tax picture is clear.
• Use T1213 only if real deductions justify it — and file early.

Next: RSUs, explained properly.