Why Most Business Owners Get ROI Wrong
Ask ten small business owners whether their Google Ads are profitable and most will say "I think so" or "I'm not sure." That uncertainty is expensive. Without knowing your actual return on investment, you're either under-spending on something that works or over-spending on something that doesn't.
The problem isn't that ROI is hard to calculate — it's that most people use the wrong inputs, track the wrong things, or forget to account for important costs. This guide walks you through the exact process, step by step.
The Google Ads ROI Formula
The basic ROI formula is:
ROI = (Revenue from Ads – Cost of Ads) ÷ Cost of Ads × 100
This gives you a percentage. If the number is positive, you're making money. If it's negative, you're losing it.
Worked Example
- Revenue from Google Ads customers: £8,000
- Total Google Ads spend: £1,200
- ROI: (£8,000 – £1,200) ÷ £1,200 × 100 = 567%
For every £1 spent on ads, you earned £5.67 in profit (before other business costs). That's a strong return.
ROAS vs ROI: What's the Difference?
You'll often see ROAS (Return on Ad Spend) used alongside ROI. The difference:
| Metric | Formula | What It Tells You |
|---|---|---|
| ROAS | Revenue ÷ Ad Spend | Revenue generated per pound spent |
| ROI | (Revenue – Ad Spend) ÷ Ad Spend × 100 | Profit percentage on your investment |
Using the example above:
- ROAS = £8,000 ÷ £1,200 = 6.67 (or 6.67:1)
- ROI = 567%
Both are useful. ROAS is simpler to calculate on the fly. ROI gives you a clearer picture of actual profitability.
The Metrics You Need to Track
To calculate ROI accurately, you need to connect your ad spend to actual revenue. Here's the chain of data you need:
1. Total Ad Spend
Found directly in your Google Ads dashboard. This is the easy part.
2. Number of Leads
How many genuine enquiries came from your ads? This requires proper conversion tracking — phone calls, form submissions, or live chat messages attributed to ad clicks.
3. Lead-to-Customer Conversion Rate
Of those enquiries, how many became paying customers? Most small businesses convert between 20% and 40% of qualified leads.
4. Average Job Value
What does each customer spend with you? If you do a mix of small and large jobs, use a weighted average over the last 6–12 months.
5. Customer Lifetime Value (Optional but Valuable)
If customers come back — annual boiler services, regular cleaning, repeat landscaping work — factor in the total value over time, not just the first job.
Step-by-Step ROI Calculation
Let's work through a realistic example for a UK electrician.
Step 1: Gather Your Numbers
| Input | Value |
|---|---|
| Monthly Google Ads spend | £800 |
| Leads generated | 22 |
| Lead-to-customer conversion rate | 32% (7 customers) |
| Average first job value | £350 |
| Average customer lifetime value (3 years) | £900 |
Step 2: Calculate First-Job ROI
- Revenue from first jobs: 7 × £350 = £2,450
- ROI: (£2,450 – £800) ÷ £800 × 100 = 206%
Step 3: Calculate Lifetime ROI
- Lifetime revenue from those 7 customers: 7 × £900 = £6,300
- Lifetime ROI: (£6,300 – £800) ÷ £800 × 100 = 688%
The difference between first-job ROI and lifetime ROI is significant. If you only look at the initial transaction, you're undervaluing your ads.
Common Miscalculations (And How to Avoid Them)
Mistake 1: Not Tracking All Conversions
If your website generates phone calls and form submissions but you're only tracking form submissions, your ROI looks worse than it actually is. For most trade businesses, 60–80% of enquiries come via phone. Without call tracking, you're missing the majority of your leads.
Fix: Set up Google Ads call tracking and use a tracking number on your landing pages.
Mistake 2: Counting Revenue, Not Profit
If a job generates £2,000 in revenue but costs you £1,200 in materials, labour, and travel, the actual value to your business is £800. Using revenue instead of gross profit inflates your ROI.
Fix: Use gross profit (revenue minus direct job costs) for a more accurate picture. Or stick with revenue but acknowledge your ROI is an upper estimate.
Mistake 3: Ignoring Management Costs
If you're paying an agency or freelancer to manage your ads, that cost needs to be included alongside your ad spend. A £500 monthly management fee on top of £800 in ad spend means your true cost is £1,300, not £800.
Fix: Add all advertising-related costs together: ad spend + management fees + any tool subscriptions.
Mistake 4: Attributing All Revenue to Ads
Did the customer find you through Google Ads, or did they see your van, get a recommendation, and then Google your name? Not every customer who clicks an ad was truly acquired through advertising.
Fix: Ask new customers how they heard about you. Use Google Ads' conversion attribution settings to understand the customer journey.
Mistake 5: Using Too Short a Time Frame
Judging your Google Ads ROI after one week — or even one month — often gives misleading results. Campaigns need time to optimise, and customer acquisition has natural variability.
Fix: Evaluate ROI over a rolling three-month period minimum. Monthly tracking is fine for trend-spotting, but don't make big decisions based on a single month.
What's a Good ROI for Google Ads?
There's no universal "good" ROI because it depends on your margins, but here are some general guidelines:
| ROI | Assessment |
|---|---|
| Below 0% | Losing money — needs urgent review |
| 0% – 100% | Breaking even or marginal — check for optimisation opportunities |
| 100% – 300% | Solid return — most well-run campaigns land here |
| 300% – 500% | Strong return — consider increasing budget |
| 500%+ | Excellent — you're likely under-spending |
For trade businesses with high job values (builders, kitchen fitters, roofers), ROI above 500% is common because even a few converted leads generate significant revenue.
For lower-value, higher-volume services (window cleaning, carpet cleaning), a 100–200% ROI is more typical and still perfectly profitable.
Building a Simple ROI Tracking System
You don't need expensive software. A basic spreadsheet works:
| Month | Ad Spend | Mgmt Fee | Total Cost | Leads | Customers | Revenue | Gross Profit | ROI |
|---|---|---|---|---|---|---|---|---|
| Jan | £800 | £400 | £1,200 | 18 | 6 | £3,600 | £2,400 | 100% |
| Feb | £800 | £400 | £1,200 | 22 | 8 | £4,800 | £3,200 | 167% |
| Mar | £900 | £400 | £1,300 | 25 | 9 | £5,400 | £3,600 | 177% |
Update this monthly and you'll spot trends quickly — which months deliver the best return, whether changes to your campaigns are working, and when it's time to scale up.
Your Next Step
Calculating your ROI isn't a one-time exercise. It's an ongoing discipline that should inform every decision about your marketing budget.
If you're not sure whether your Google Ads are actually making you money — or you suspect they could be doing better — request a free audit from SwiftLead. We'll connect the dots between your ad spend and your revenue, identify where you're leaking budget, and show you exactly what your true ROI looks like.
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