How Do You Know When You're Spending Too Much on Ads?
There's a version of this business that feels like it's working right up until it doesn't: revenue climbing every month, ad spend climbing alongside it, and a bank balance that somehow never grows.
The number that tells you which side of the line you're on is your break-even ROAS, and most stores have never calculated it.
What is break-even ROAS?
The return on ad spend at which you make exactly nothing. Above it you're profitable; below it you're paying for revenue.
Break-even ROAS = 1 ÷ contribution margin %If your contribution margin is 30%, break-even ROAS is 1 ÷ 0.30 = 3.33.
Meaning every $1 of ad spend needs to return $3.33 in revenue just to break even. At 3.0 ROAS — which sounds healthy, and which plenty of owners would be pleased with — you are losing money on every sale.
This is the single most useful number in ecommerce advertising and almost nobody has it written down.
Work out yours
Take contribution margin (gross profit minus payment fees and shipping, before ad spend):
| Contribution margin | Break-even ROAS |
|---|---|
| 20% | 5.00 |
| 30% | 3.33 |
| 40% | 2.50 |
| 50% | 2.00 |
| 60% | 1.67 |
Swipe to see more →
Two things follow immediately.
Thin margins make advertising nearly impossible. At 20% contribution margin you need 5x ROAS, which very few stores sustain. If that's you, the fix is pricing or costs — not better ad creative.
A "good" ROAS is meaningless without your margin. A 3.0 ROAS is excellent at 50% margin and loss-making at 25%. Anyone who tells you a target ROAS without asking your margin is guessing.
What are the warning signs?
Revenue up, profit flat or down. The clearest signal, and the one that requires actually tracking profit to see. If revenue grew 40% and profit grew 0%, the growth was purchased.
Rising blended cost of acquisition. If total ad spend divided by total new customers keeps climbing, you're paying more for the same result. Some of that is normal as you exhaust the cheapest audience — a lot of it isn't.
You can't remember the last time you had spare cash. Growing businesses tie cash up in stock, so this isn't conclusive on its own. But combined with the above it usually means margin is going out the door.
Your best ROAS campaign is your branded one. People searching your brand name were going to buy anyway. If that campaign is propping up your blended numbers, your actual acquisition performance is worse than it looks.
You keep raising budget to hit revenue targets. Revenue targets set without a margin constraint always end here.
What about lifetime value?
The standard rebuttal: "I can afford a lower ROAS because customers come back."
Sometimes true. But two conditions have to hold, and usually only one is checked.
You need actual repeat data. Not a hope. Do your customers genuinely reorder, at what rate, and how soon? If you've been trading eighteen months and haven't measured it, you don't know.
You need to survive the gap. Even with genuine repeat purchase, you pay the acquisition cost today and receive the second order in six months. Cash-flow death is a real way profitable-on-paper businesses fail.
A reasonable rule: be profitable on the first order, or be very sure about your repeat rate. Buying customers on a promise is a strategy for businesses with funding.
When is high ad spend actually fine?
Not all overspending is a mistake. It's legitimate when:
- You're deliberately buying data. A capped test budget to learn whether a channel works is an investment, provided it's capped and time-boxed
- You're clearing stock. Selling below margin beats holding dead inventory
- You have proven repeat purchase and the cash to bridge the gap
- You're launching, and building an audience worth more later
The distinction is always the same: did you decide to do this, or did it happen? Deliberate loss-making with a stopping rule is strategy. Drifting into it is the thing that closes businesses.
How to actually watch it
Three numbers, monthly:
- Contribution margin % — so you know your break-even ROAS
- Blended ROAS — total revenue ÷ total ad spend, all platforms
- Profit, not revenue — the one that settles the argument
The awkward part is that these need Shopify, your supplier costs, your courier and every ad platform in one place. Doing it by hand monthly is a real chore, which is why it usually stops after two months.
That's what Rev Room automates for NZ and Australian stores — blended ROAS across Meta, Google and TikTok alongside true contribution margin, so the comparison is in front of you rather than something you rebuild each month.
The short answer
- Break-even ROAS = 1 ÷ contribution margin. Calculate it today
- A "good" ROAS means nothing without knowing your margin
- Warning signs: revenue up while profit is flat, rising acquisition cost, branded campaigns flattering your blended numbers
- LTV justifies lower ROAS only with measured repeat rates and the cash to bridge
- Deliberate overspending with a stopping rule is fine; drifting into it isn't
Related reading: Blended ROAS across ad platforms · How to calculate your profit margin properly · When should you be running Meta ads?
General information only, current as at 20 August 2026. Figures are illustrative.