My friend told me his retirement number, and I asked him one question.

It's the question that quietly breaks most retirement math. The good news is the fix is simpler than it sounds.

I was driving through Montreal a couple weeks ago with a buddy who sold his company last year. He’s in that good, restless headspace where he’s finally had a win after years of grinding and figuring out what’s next. Somewhere near the bridge where we were backed up because of the Grand Prix, he asked me the question I see online about four hundred times a day:

“What’s your retirement number?”

He had one in his head. A real, specific number. So I asked him the only thing that matters before you trust a number like that:

“Is that in today’s dollars?”

Pause. Then — “…oh.”

That little “oh” is the whole reason I wrote this one.

Your number today is not your number in the future

Here’s the thing nobody puts on the rule-of-thumb lists. A retirement number is almost always quoted in today’s money (what your life costs right now). It’s a clean way to think about it. But you’re not retiring today.

Earlier in this series, we worked out that a certain household needs about $1.73 million to fund the retirement they want. In today’s dollars.

Inflate that forward to the day they actually retire, let’s say…thirty years out, and the same exact life (same groceries, same vacation and the same utility bills) costs about $3.14 million.

Nothing got fancier. They didn’t add a boat. That extra million-and-change is just inflation wearing a Halloween costume. But if you saved toward the $1.73 million and called it a day, you’d quietly aim about a 50% low and not find out for decades.

That’s the trap. And once you see it, you can’t unsee it.

The good news is the boring news

So the future number is bigger.

Take a deep breath. It’s ok…

Because the way you get there is more in your control than the number itself.

You don’t need heroic investment returns unless it’s hail mary time. You just need time. And time in in the investment world is non-linear, in a way that’s either great news or a kick in the teeth depending on when you start.

Check out the same target as before, but start at 25. Then it takes roughly $1,900 a month. Start the same plan at 45, and it takes about $5,400 a month to land in the exact same place.

Same finish line. Nearly triple the monthly cheque. The only thing that changed was twenty years.

That gap isn’t a willpower problem. It’s compounding. The dollars you put in early are the only ones that get to sit and grow for decades — and in that example, about 40% of the final pile is growth the household never actually deposited. Money the money made, mostly off the early contributions.

Investment returns are important, but it’s not the ‘be all, end all’

Everyone wants to argue about returns. 6% or 7%? What’s the sexy new investment? Quantum computing or go 100% XEQT because it’s going to have another 30% year? It’s the most fun part to obsess over and the least important lever you’ve got. You don’t control the market anyway.

You do control when you start and how much you put away. Those two beat fund-picking, every time. Starting beats optimizing. Boring, true, and weirdly freeing.

The part the math can’t do

You’ve now got the number and the path to it. Which leaves the only question that was ever actually interesting, and the one Part 5 is about: what’s all of it for?

The spreadsheet can tell you the number. It cannot tell you what the money is for. That part’s yours.

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I wrote the full version — with the actual formulas, the CPP and OAS piece, and a table of what waiting costs you decade by decade — on the site:

→ Read the full breakdown on YouGotThis

And if you’d rather just see your own numbers instead of mine — current savings, what you’re putting away, the inflation-adjusted target for the year you’ll actually retire — that’s literally the thing I built:

→ Run your numbers (free)

— Andrew

Andrew Gannon, CFA, is the founder of YouGotThis. Educational illustration only — not financial, investment, tax, or legal advice. The figures use simplifying assumptions and are there to build intuition, not to size anyone’s strategy.