What this retargeting calculator works out
Retargeting (remarketing) only works on people you can still recognise. This calculator starts from your traffic, applies a realistic match rate, and returns the three numbers that decide whether a campaign is worth running: how many people you can reach, what it costs, and what comes back.
Step 1 — Addressable audience
Not every visitor becomes a targetable user. Browser privacy limits, blocked third-party cookies, and people who clear storage all shrink the list. Match rate is the share you can still serve ads to — often 40–60% for display, higher on logged-in platforms like Meta or Google.
Addressable audience = monthly visitors × (window ÷ 30) × match rate
The window matters because audiences expire. A 30-day window on 50,000 monthly visitors covers roughly the whole month. A 7-day window covers about a quarter of it — a smaller but much warmer list.
Step 2 — Impressions and budget
You pay per impression, not per person.
Impressions = audience × frequency Budget = (impressions ÷ 1,000) × CPM
Retargeting CPMs vary widely by platform and format. Display is usually cheaper than social feeds; video costs more than static.
Step 3 — What comes back
Conversions = audience × conversion rate Revenue = conversions × average order value
Retargeting conversion rates look impressive next to cold traffic, because the audience already knows you. That is also the trap.
The incrementality trap
A retargeting campaign can report a 4x ROAS and still add almost nothing.
The people who see your retargeting ads are, by definition, the people most likely to buy anyway. If you retarget everyone who visited in the last 30 days, a large share of those "conversions" would have happened without the ad. You end up paying to be credited for demand you already created.
Two things fix this:
- Exclude recent purchasers and anyone who already converted.
- Run a holdout. Keep 10% of the audience out of the campaign and compare conversion rates. That gap is your true incremental lift.
Use this calculator for planning audience size and budget. Use a holdout to find out whether the ROAS is real.
Retargeting vs prospecting
| Prospecting | Retargeting | |
|---|---|---|
| Audience | People who don't know you | People who already visited |
| Conversion rate | Low | Much higher |
| Ceiling | Large | Limited by your traffic |
| Real risk | Wasted spend | Paying for demand you already had |
Retargeting cannot scale past your own traffic. If monthly visitors are small, the addressable audience is small and the budget is small with it — that is a ceiling, not a failure. Raise conversion rate and AOV so each retargeted visit is worth more, and check CPM and CPC to judge whether the media itself is priced sanely. Compare the result against blended ROAS — if retargeting ROAS is high but blended ROAS is flat, you are mostly harvesting existing demand.