“Does size matter?” when it comes to backtesting?

It’s the kind of question that gets a few smirks, sure. But when it comes to backtesting trading strategies, it’s not a joke, it’s the difference between confidence and false hope.

Let’s get real for a minute: the size of your candles absolutely matters.

What you don’t see can hurt you
Most people start testing on bigger timeframes. It’s faster, easier on the eyes, and the results look clean. But clean doesn’t mean correct.

Larger candles blur the details. That one nice-looking 4-hour candle? Inside, price could’ve spiked, reversed, chopped around, or triggered your stop before closing where it did. You’d never know. And that’s the problem.

You might think your entry worked beautifully… but only because the data smoothed out everything that actually happened.


A backtest should feel like a real trade
Trading isn't just about the final price. It’s about what price does to get there. That messy movement inside the candle? That’s where most trades are made or broken.

If your strategy is even remotely reactive, waiting for structure, confirmation, retests, or anything time-sensitive, you need to see what price did between the open and close.

And the only way to see that? Use smaller candles.


Smaller data, clearer picture

1-minute candles might look overwhelming at first, but they give you something the higher timeframes just can’t: behavior.

Not just outcomes. Not just win/loss stats. But the actual shape of the move, the hesitation, the fakeouts, the precise moment when the trade made sense—or didn’t.

And once you start testing with that level of detail, your strategy either earns your trust… or shows its cracks.


So how small should you go?
There’s no one-size-fits-all here. But as a general rule: if your idea relies on precision, go small. Test it on 1-minute or 5-minute charts, even if you plan to execute on higher timeframes. You’ll quickly see if the entry makes sense, or if you’ve been relying on candle-close hindsight.

Yes, it takes longer. Yes, you’ll stare at noisy charts for hours. But your strategy will thank you.


Watch out for “too good to be true”
One last thing, if your backtest results look flawless on 1h or 4h candles, pause. That’s often a sign that you’re testing a story, not a strategy.

Zoom in. See what actually happens. You might be surprised at how different the same trade looks when you’re not glossing over the details.

TL;DR:
In backtesting, size absolutely matters. Smaller candles reveal real behavior. Bigger ones hide the truth. So if you care about how your strategy actually performs not just how it looks.
go smaller. Your backtesting will get sharper, and your confidence? Way more earned.