It is the most common question in digital marketing: should you invest in SEO (organic search) or SEA (Google Ads)? The answer depends on your objectives, your budget and your time horizon. They are not competitors: they are two complementary approaches with radically different logic.
At ConvertiLab, we have run SEO and SEA strategies for 150+ clients since 2021. Here are the concrete rules for choosing, and for knowing when to combine the two.
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What are the concrete differences between SEO and SEA in cost and in results?
SEO generates organic traffic, free per click, but it takes 3 to 12 months before you see meaningful results. SEA generates traffic immediately, but every click has a price (0,30€ to 50€ depending on the sector) and the traffic stops the moment you cut the budget. On long-term ROI, SEO wins every time, but SEA is irreplaceable for a launch or a time-limited promotion. A rule often quoted: if your horizon is 6 months, choose SEA; if your horizon is 18 months, choose SEO; if your horizon is both, start with SEA and build SEO alongside it.
| Criterion | SEO | SEA |
|---|---|---|
| Time to results | 3 to 12 months | A few hours |
| Cost per click | 0€ once you rank | 0,30€ to 50€ by sector |
| Durability | Lasts even if you stop | Traffic = 0 if the budget is cut |
| Average CTR | Position 1 = ~27% | ~3 to 5% on ads |
| User trust | Strong (an "earned" result) | Moderate (some people ignore ads) |
| Scalability | Cumulative (snowball effect) | Linear (+ budget = + traffic) |
When should you choose SEO and when should you choose SEA for your business?
SEO is ideal when your marketing budget is limited over the long run, when CPCs in your sector are high (trades, legal, medical), when you can wait 3 to 6 months for results, and when you want to build lasting brand authority. SEA is ideal when you are launching and need traffic straight away, when you have a time-limited event or promotion, or when you want to test a market before investing in SEO. In practice, 90% of the business owners we work with end up with both channels running: the question is not "one or the other" but "in what order and in what proportions".
When to favour SEO:
When to favour SEA:
How do you combine SEO and SEA to maximise your return on investment?
The winning strategy in 2026 is to combine SEO and SEA according to your stage of development. Phase 1 (months 1-3): SEA dominant, to generate traffic immediately while SEO is being built. Phase 2 (months 4-8): both channels in parallel, using the SEA data, meaning the keywords that convert, to steer the SEO strategy. Phase 3 (month 9 onwards): cut the SEA budget on keywords that already rank organically and keep the ads running on high-CPC or highly competitive queries.
The concrete synergies between SEO and SEA:
A ConvertiLab case: a self-employed chartered accountant in Rennes had a marketing budget of 1 500€/month, all of it in SEA. He was getting 15 leads a month at 100€ a lead. After 6 months of gradual rebalancing (900€ SEA + 600€ SEO), his organic rankings brought in 8 extra leads a month at a marginal cost close to 0. In total: 23 leads a month on the same budget, 53% more. 12 months on, with the SEO positions consolidated, the SEA budget was down to 600€ for 28 leads a month, and the cost per lead had been divided by 2,5.
The sectors where SEO clearly beats SEA
In some sectors, Google Ads CPCs are so high, 10 to 50€, that SEO becomes the only viable channel for a small business on a limited budget.
Sectors with very high CPCs, where SEO comes first:
In these sectors, a SEA budget of 1 000€/month buys only 20 to 200 clicks. By comparison, a top organic ranking can bring 500 to 2 000 visits a month at no marginal cost. The maths is simple: put the same budget into SEO and the effect compounds.
Sectors where SEA still makes sense:
A comparative ROI example, for a typical ConvertiLab client:
SEO has the better long-term ROI, but SEA lets you generate revenue from the very first month.
Frequently asked questions about choosing between SEO and SEA
Can you do SEO with no budget?
Yes, but it is slow. You can optimise your site yourself, from tags to content to speed, at no direct cost. The investment will be time rather than money: expect 5 to 10 hours a week to see results in 6 to 12 months. If you put a value on your time, professional support will speed the process up considerably. Our free SEO audit identifies the priority fixes so you start on solid ground. Once you factor in the hourly cost of your own time, "free" DIY SEO often costs more than delegating to a professional.
Does Google Ads cannibalise SEO traffic?
No. Studies show that sites present in both the organic and the paid results get more total traffic than the two channels deliver separately. Appearing in both places strengthens trust and lifts the overall click-through rate. It is still smart, though, to cut your SEA spend on keywords where your organic position is already strong, in positions 1 to 3.
What is the minimum budget to start with Google Ads?
You can start with 300 to 490€ a month to test a market, but meaningful results usually arrive from 1 000€/month. The right budget depends on the average CPC in your sector: divide your budget by the CPC to estimate the number of clicks. Aim for at least 30 to 50 clicks a day so you have usable data and can make reliable optimisation decisions.
Does SEA help SEO indirectly?
Indirectly, yes. The traffic SEA generates raises your brand awareness, and some visitors come back by typing your name straight into Google, which improves your brand signals. On top of that, the conversion data from your Ads campaigns shows you which keywords carry strong commercial intent, and that guides your SEO content strategy. But there is no direct link between Google Ads spend and organic rankings: they are two completely separate algorithms. !SEA brand awareness, brand signals, direct queries, indirect impact on SEO
