"Narrow targeting is more accurate" and "broad is the answer these days" both circulate at the same time. Both are true, and both are half-true. The right answer changes with the situation, so this isn't something to memorize — it's something to learn to judge. Today, let's look at what to check before you decide.

Narrowing gets you accuracy, but it costs more and burns out faster

Let's start with the tradeoff. Narrowing your targeting gives you something and takes something away at the same time.

A table comparing narrow and broad targeting across four factors. Narrow targeting has smaller reach, more expensive CPM, and higher conversion rate, but exhausts the audience faster. Broad targeting has larger reach, cheaper CPM, and lower conversion rate, but exhausts more slowly.

Narrow it down, and conversion rate goes up — makes sense, since you've picked only the people likely to care. But you lose three things in exchange: the number of people you can reach shrinks, CPM gets more expensive (more advertisers competing for the same slice), and you run out of people to show it to much faster.

Broaden it, and it's the opposite. CPM is cheap and there are plenty of people, but uninterested people get mixed in too, so conversion rate drops.

Here's the key point: CPA is the outcome of all four of these interacting together. If you look only at conversion rate and conclude "narrower is better," you're missing the CPM increase. If you look only at CPM and conclude "broader is better," you're missing the conversion rate drop. You need to judge by final CPA, not by any single metric in isolation.

When budget scales up, narrow targets break

This is where things fall apart most often in practice — a narrow target that's been performing well suddenly collapses in efficiency the moment you increase its budget.

A diagram showing that at a daily budget of $150, impressions land reasonably on a narrow target, but raising the daily budget to $1,500 on the same narrow target causes impressions to pile up excessively, spiking frequency.

The reason is simple. If the audience size stays the same but the budget goes up, that extra money gets spent showing the ad more often to the same people. Frequency spikes. And once frequency spikes, creative fatigue arrives fast — CTR drops, CPM rises, and CPA collapses.

So here's a principle: audience size should scale with budget. If you're raising budget, either widen the audience alongside it or rotate creative more frequently. Raise the budget and leave everything else unchanged, and it breaks almost every time.

So what should you actually check

Three things, roughly, and the picture becomes clear.

One, what's frequency doing right now? If frequency keeps climbing, that's a sign the audience is too narrow — time to widen it. If frequency is staying low, there's still room.

Two, are you planning to raise budget? If you are, it's safer to widen the audience ahead of time. If you wait to react until after CPA spikes post-increase, you've already burned several days' worth of spend.

Three, how much conversion data have you accumulated? This matters more than people realize. Ad platform algorithms need a certain volume of conversion data to learn well, and if the target is too narrow, conversion counts stay low and learning suffers. In this case, widening actually improves accuracy — narrower isn't always more precise.

Why you shouldn't take a narrow target's great CPA at face value

One thing worth flagging directly. Very narrow targets — retargeting being the classic case — often show dazzling CPA numbers. But taking that number at face value is risky.

These are people who already visited your site. A good chunk of them would have come back anyway, even without seeing the ad. The ad is just stamping a receipt on a conversion that was already happening. That's why retargeting CPA tends to look better than the actual incremental impact it delivered.

To filter this out, you need incrementality measurement. The narrower the target, the bigger this distortion tends to be — so it's worth second-guessing the instinct to say "CPA looks great, let's pour more into this."

The answer isn't one or the other — it's a mix

In practice, this is usually how it plays out.

You build scale on broad targeting, and pull efficiency from narrow targets (retargeting, lookalikes). It's not a matter of picking one — it's a matter of what ratio you blend them in.

And that ratio isn't fixed. As budget grows, the broad side needs to carry more weight; as an audience exhausts, you need to open up new targets. Ultimately, the job comes down to checking whether each target is currently saturated or not, and reallocating budget accordingly.

Try this today

Line up your current campaigns by targeting width, and write down the frequency for each one alongside it.

If there's a narrow target where frequency keeps climbing, that's the one about to break. If you're planning to raise budget and the target is narrow, widen the audience before you raise the budget — not after. Just reordering those two steps saves you several days of wasted spend.

Wrap-up

Narrow versus broad isn't a matter of preference. Decide based on what frequency looks like right now, whether you're about to raise budget, and whether you have enough data. And it's worth second-guessing a narrow target's great-looking CPA, at least once.

Figuring out whether a CPA collapse is really about targeting, creative, or budget allocation is a separate question — pick that up in how to lower CPA.