How to Set a Google Ads Budget: A Practical Guide
Short answer: Budget = target CPA × conversions you want per month. Want 30 conversions at $50 CPA? You need $1,500/month. Don’t pick a budget randomly — anchor it to your unit economics so every dollar has a defined purpose.
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Step 1: Calculate your break-even CPA first
Before setting a budget, you need to know the maximum CPA you can afford. This is your gross profit per conversion:
- Break-even CPA = AOV × gross margin %
- Example: $120 AOV × 35% margin = $42 break-even CPA
- Set your target CPA below $42 to ensure profitability
Use our break-even CPC calculator to find your exact numbers. See what is break-even CPC for the full explanation.
Step 2: Set a monthly budget from your CPA target
- Monthly budget = target CPA × target monthly conversions
- Example: $35 target CPA × 40 conversions/month = $1,400/month
- Daily budget: $1,400 ÷ 30.4 days = $46/day
This gives you a budget that’s directly tied to a business outcome. If you hit your CPA target, the budget pays for itself. If you can’t afford the calculated budget yet, reduce the target conversion volume and scale up as results prove out.
Use our ad budget forecast calculator to model expected clicks, conversions, and profit from any budget.
What’s a realistic starting budget?
- Minimum viable test budget: $20–50/day ($600–1,500/month). Below this, you’ll get too few clicks to collect meaningful data in 30 days.
- To use Smart Bidding (Target CPA): You need 30–50 conversions per month. Budget accordingly — if your CPA is $50, you need at least $1,500/month to hit the minimum conversion threshold.
- Competitive verticals (legal, finance): $50–$200+/day minimum to get statistically meaningful data, given high CPCs.
How Google’s daily budget actually works
A few things most advertisers don’t realise:
- Google can spend up to 2× your daily budget on high-traffic days, but will stay within your monthly budget cap (daily budget × 30.4)
- If your campaign shows “Limited by budget,” you’re missing eligible auctions — check Impression Share lost to budget
- Budget is set at the campaign level, not the ad group or keyword level
- Pausing a campaign doesn’t refund unused daily budget — set budget adjustments instead for periods of lower activity
Budget allocation across campaigns
If you’re running multiple campaign types, a typical starting allocation for ecommerce is:
- Google Shopping / Performance Max: 50–60% of budget (highest purchase intent)
- Google Search (non-branded): 25–35% (high intent, text-based)
- Branded search: 5–10% (protect your brand from competitors)
- Display / YouTube: 0–15% (awareness, only once Search is profitable)
Signs your budget is too low
- Campaign status shows “Limited by budget”
- IS lost to budget exceeds 20–30%
- Daily budget exhausts before noon in your target timezone
- Fewer than 5–10 clicks per day per campaign
- You haven’t hit 30 conversions in 60+ days (Smart Bidding can’t learn)
Signs your budget might be too high
- Campaign never reaches daily budget limit and IS is already 85%+
- CPA is rising despite no changes — you may be reaching lower-intent audiences as the algorithm exhausts high-intent traffic
- You’re profitable and hitting CPA targets — in this case, it’s a scaling question, not a budget problem
Common mistakes
- Setting budget without calculating break-even CPA first. A $500/month budget might be too little or too much depending on your CPCs and margins. Always start with unit economics.
- Spreading thin budget across too many campaigns. 10 campaigns at $50/day each = 5 clicks per campaign per day. Consolidate to 2–3 campaigns at $150–$250/day and get enough data to optimise.
- Cutting budget when CPA is high. Budget cuts reduce data volume, making it harder to diagnose and fix the real problem. Instead, pause underperforming keywords and reallocate within the same budget.
FAQ
Should I set a shared budget or individual campaign budgets?
Individual campaign budgets give you more control and visibility. Shared budgets let Google redistribute across campaigns but can cause one campaign to consume most of the budget. Use individual budgets unless you specifically want Google to balance between campaigns.
How often should I adjust my budget?
Don’t change budgets daily. Review weekly and make adjustments if campaigns are consistently maxing out budget (increase) or consistently underspending at good CPA (scale up or diagnose why IS isn’t higher).
Does increasing budget improve performance?
Only if the campaign is limited by budget (IS lost to budget is high). If IS lost to budget is low, more budget won’t help — the constraint is ad rank or conversion rate, not money.