How to track the ROI of your advertising spend (and prove it to your accountant)

Almost every construction business owner we work with can answer the question "how much do you spend on advertising per month?". Far fewer can answer the one that actually matters: "how much revenue does every euro spent generate, channel by channel?". Without that answer, the marketing budget gets managed by gut feeling — cut when things go badly, increased when things go well, without really knowing what caused what.

In this guide we explain the method we use to track the real ROI of our clients' advertising campaigns, and a side benefit that's often overlooked: the same reporting used to measure ROI is exactly what's required to document the tax deductibility of the expense.

1. Why most SMEs don't track real ROI

The problem isn't a lack of data — Google Ads and Meta Ads provide dozens of metrics in real time — but its fragmentation. The advertising platforms know how many clicks and leads they generated, but not how many of those leads later became paying customers, or how much they spent. The salesperson knows who signed a contract, but often doesn't know which campaign that customer came from.

The result is that a great many construction businesses know their cost per lead but not their real ROI: two completely different numbers. A channel with a low CPL but full of leads that don't qualify can have a worse ROI than a channel with a higher CPL but higher-quality customers.

2. ROI and ROAS: two different metrics, two different uses

A practical example: a Meta Ads campaign costs €3,000 and generates €24,000 in signed contracts. ROAS is 8x (24,000 ÷ 3,000). ROI is instead 7x ((24,000 − 3,000) ÷ 3,000). The difference looks small on a single channel, but becomes significant when comparing multiple campaigns with very different costs.

3. What you need to track ROI correctly

• 1
  Attribution of the lead to its originating campaign

  Every contact must enter the system already tagged with the channel, campaign and ad it came from.
• 2
  Connection between the lead and the sales pipeline

  The lead must stay tracked from entry through to the final outcome: quote, signed contract, or lost.
• 3
  Contract value linked to the lead

  Signed revenue must be recorded and linked to the originating lead, not just tracked as an aggregate number.
• 4
  Ad spend per channel for the same period

  You need to compare spend and revenue over the same time frame, not misaligned periods.

4. How a CRM connects ad spend and revenue

A CRM properly configured for marketing solves the fragmentation problem: every lead enters the system with a source tag (Google Ads, Meta Ads, referral, organic site), gets followed through the entire sales pipeline — qualification, site visit, quote, close — and the revenue from the signed contract stays linked to that source tag until the end.

The result is a dashboard that shows, for every channel, not just how many leads it generated but how much real revenue it produced — letting you shift budget from less profitable channels to better-performing ones, instead of deciding based on cost per lead alone.

5. The connection to tax deductibility

Here's the point that's often overlooked: the documentation needed to deduct advertising expenses at 100% — media plan, performance reports, proof of the link between spend and business activity — is exactly what an ROI tracking system produces as a byproduct of its normal operation.

Anyone already tracking marketing with a structured CRM has, with no extra effort, the monthly per-channel reports that show where the budget was invested and what commercial results it generated — the very same evidence required in the event of an audit into the deductibility of the expense. Measuring ROI and documenting tax deductibility, in practice, require the same system.

6. The metrics to monitor beyond ROI

Monitored together, rather than in isolation, these metrics enable correct decisions: a channel with a low CPL but a poor closing rate can be worth less than a channel with a higher CPL but higher-quality customers and a higher average contract value.

Conclusion: without tracking, marketing is a gamble

Spending on advertising without tracking real ROI means making budget decisions based on intuition, not data. A system that links every lead to its origin and the revenue it generates turns marketing from an uncertain expense into a measurable investment — and, as an added benefit, automatically produces the documentation required for the tax deductibility of the expense.

If today you can't confidently answer which channel is generating your company's revenue, that's the first problem to solve before deciding where to cut or where to invest more.