How to choose subreddits for Reddit ads

Start from the communities where your buyers already describe the problem you solve, not the biggest subreddits in your category. Pick only as many as your budget can test fairly (about 2.3 times your target cost per conversion each), group similar ones so the report is readable, then move budget to the ones that prove themselves.

Updated 28 September 2026

Start from the problem, not the category

Typing your category into the targeting search box and picking the top results gets you the biggest, most general subreddits. They have the most inventory, so they'll take most of your budget, and their members are often there for news or memes rather than to solve the problem you solve.

Instead, search Reddit for the phrases your customers use when they have the problem: "how do I invoice international clients", "best way to track macros", "alternative to [competitor]". Note which communities those threads live in. Those are your candidates, even if they're small.

Size the list to your budget

Each subreddit needs roughly 2.3 times your target cost per conversion before a zero means anything (here's why). Divide your test budget by that number to get how many subreddits you can test.

Subreddits you can test ≈ test budget ÷ (2.3 × target cost per conversion)

With $1,000 and a $60 target, that's about seven. Rank your candidates by how directly their members talk about your problem and keep the top seven.

Group them so you can read the results

• Similar communities together. r/freelance and r/freelanceWriters can share an ad group and an ad. r/freelance and r/personalfinance probably shouldn't.
• Big ones on their own. A large general subreddit will dominate any ad group it's in. Give it its own so it can't hide the smaller ones.
• One message per group. Write the ad for the people in that group. It's the cheapest way to make a subreddit perform.

Mind the size trade-off

Large subreddits deliver volume but tend to be pricier per impression and less specific. Small communities are often cheaper and more relevant but can run out of people to show ads to. Most accounts end up with a couple of mid-sized communities doing the heavy lifting and a handful of small ones topping up.

Graduate the winners

Once each subreddit has had its test budget, export the community report and sort them into cut, spend more, and keep testing. Move budget from the first pile to the second. Keep 10–20% of spend for testing new communities, because audiences shift and today's winner fades.

Look at your winners for patterns. If three small, problem-focused subreddits beat the big general one, the next candidates to test are more small, problem-focused subreddits.