Key takeaways
- Your budget should be driven by unit economics, not a percentage someone made up.
- Know your customer lifetime value and target cost per acquisition before you spend.
- Start with a 'data budget' big enough to learn, then scale on proven ROAS.
- Profitable campaigns should scale up; the limit is profitability, not a fixed cap.
There's no universal right number for an ad budget — only the right number for your business. The good news: once you know a few of your own figures, the answer becomes obvious. Let's build it from the ground up.
Start with what a customer is worth
Before budgets, you need two numbers:
- Customer Lifetime Value (LTV): the total profit an average customer brings over the whole relationship — not just the first sale.
- Target Cost Per Acquisition (CPA): the most you're willing to pay to win one customer while staying profitable.
If a customer is worth NZ$1,500 in profit over time, you can comfortably spend a few hundred dollars to acquire one. If they're worth NZ$80, your maths is very different. Everything flows from this.
The number most people skip
Lifetime value, not first-sale value, is what determines how aggressively you can advertise. Businesses that only count the first purchase chronically under-invest and lose to competitors who don't.
Phase 1 — The data budget
When you launch, you don't yet know your true cost per customer on a channel — so the first budget's job is to find out. Spend enough to generate statistically meaningful results: as a rule of thumb in NZ, aim for enough budget to produce at least 15–30 conversions before judging a campaign. For many SMBs that's around NZ$1,000–$2,000 per channel per month for a month or two.
Resist the urge to declare victory or defeat after three days. Early data is noisy.
Phase 2 — Read the verdict
- 1Calculate your actual CPA: total spend ÷ customers won.
- 2Compare it to your target CPA from your unit economics.
- 3If actual CPA is comfortably below target — you have a profitable machine. Scale it.
- 4If it's above target — fix the funnel (targeting, ad, landing page, offer) before spending more.
Phase 3 — Scale on profit, not fear
Here's the mindset shift: if every NZ$1 you put in reliably returns NZ$3 in profit, the question isn't 'what's my budget?' — it's 'why would I stop?' Profitable campaigns should be scaled until they stop being profitable, watching for diminishing returns as you push into broader, more expensive audiences. Increase budgets in steps (20–30% at a time) so the platforms can adjust without resetting their learning.
“A budget isn't a ceiling you set out of fear — it's a dial you turn while the maths keeps working.”
— Navbar Digital
What about the '5–10% of revenue' rule?
Generic benchmarks like 'spend 5–10% of revenue on marketing' are fine for a sanity check, but they ignore your margins, your LTV and your growth stage. A high-margin business chasing growth should often spend more; a thin-margin one, less. Use your own economics first and benchmarks second.
Frequently asked questions
How much should a small business spend on paid ads?
Enough to learn, then enough to scale profitably. Start with around NZ$1,000–$2,000 per channel per month to gather meaningful data, then scale based on whether your actual cost per acquisition beats your target. The right number is driven by your unit economics, not a fixed percentage.
How do I know if my ad budget is working?
Compare your actual cost per acquisition (total spend ÷ customers won) to your target CPA from your lifetime value. If actual CPA is comfortably below target, the campaign is profitable and worth scaling. If it's above, fix the funnel before adding budget.
Should I scale a profitable ad campaign?
Yes — until it stops being profitable. Increase budgets in 20–30% steps so the platform's optimisation keeps up, and watch for diminishing returns as you reach broader, more expensive audiences.
