It's the question we get asked most often in a first meeting with a new client, and also the one we least enjoy answering with an exact number, because any figure thrown out without context is, at best, a rough average. But the alternative (giving no reference at all) doesn't help anyone plan either, so it's worth breaking down what actually determines the minimum viable budget: the cost of each conversion in your sector, and how many conversions the algorithm needs in order to learn.
The logic behind the number, before the figures
Every minimum viable budget starts from the same question: on average, how much does it cost to get a conversion in your sector, and how many conversions do you need per month for the platform to have enough data to optimise well? Most of Google and Meta's automatic bidding algorithms start performing reliably from around 15-30 conversions a month per campaign. Below that, the campaign can still work, but the improvement automation can deliver is limited because it doesn't have enough data.
Consumer ecommerce (fashion, home, beauty, food)
With an average cost per click of between 0.30 and 0.80 euros and a typical online store conversion rate of between 1% and 3%, generating 20 sales a month usually requires a monthly budget of between 400 and 900 euros, depending on the product's price and the specific niche's competitiveness. Highly contested categories (generic fashion, supplements) tend toward the upper end of that range; more specific niches with less competition can work with less.
Local services (clinics, workshops, academies, hospitality)
Here the minimum budget is usually lower in absolute terms because the geographic radius is limited and competition for local keywords is lower than in a national market. Between 250 and 500 euros a month is usually enough to generate a reasonable volume of enquiries or bookings in most mid-sized cities, though in big capitals with a lot of direct competition (Madrid, Barcelona) that figure can double.
B2B and high-ticket professional services (consulting, enterprise software, machinery)
Although the required conversion volume is lower (sometimes 5-10 qualified leads a month is enough business to close several high-value sales), cost per lead in competitive B2B sectors can be considerably higher, between 30 and 150 euros per qualified contact depending on the sector. This puts a reasonable minimum budget between 500 and 1,500 euros a month, though the return per closed sale usually offsets that higher entry cost.
Online training and info-products
This sector usually has a relatively low cost per click, but a longer conversion funnel (webinar, lead magnet, email sequence before the sale), so the minimum budget needs to account not just for lead-capture advertising but also for the time (several weeks) that funnel takes to mature before generating sales. Starting with less than 300-400 euros a month usually leaves very little room to nurture the middle stage of the funnel while sustaining lead capture.
What happens if your budget falls below these figures
It doesn't mean you shouldn't advertise, it means the strategy needs adjusting: instead of spreading a small budget across several campaigns or platforms, concentrate it all in a single campaign very tightly targeted at the most profitable keyword or audience, accepting less volume in exchange for more control and ensuring the little budget available does generate useful learning. It's also worth extending the evaluation period: with tight budgets, more weeks are needed to accumulate enough data before deciding whether something works.
The cost nobody counts: management time
On top of media budget (what you pay Google or Meta), you need to add, even though it never shows up as a separate line in any report, the time spent managing the campaign, or the cost of hiring someone to do it. With very small budgets, this management cost can represent a disproportionate share of the total, which sometimes makes it more profitable to wait until you've saved up a somewhat larger budget before starting, rather than launching with the bare minimum and diluting the result in management time that never gets recovered.
An example of calculating your own minimum budget, step by step
Instead of starting from the reference figures above as-is, it's worth calculating your own business's number with a simple exercise. First, calculate your average margin per sale or per customer (price minus cost). Second, decide what percentage of that margin you're willing to spend acquiring each new customer (a reasonable reference, though it varies a lot by sector, is between 15% and 30% of the first order's margin or first contract's value). Third, multiply that figure by the minimum monthly conversion volume you need for the algorithm to learn well (15-30, as explained above).
An example with real numbers: a sports supplement store with an average margin of 12 euros per order, willing to spend 25% of that margin on acquisition (3 euros per order), needing 20 conversions a month for the campaign to learn well, arrives at a theoretical minimum budget of 60 euros... a figure that in practice wouldn't come close to covering that sector's real cost per conversion. That gap is the signal that either the margin per order is too low to sustain profitable paid advertising at that volume, or the average order value needs working on first (raising the price, selling in bundles, encouraging repeat purchases) before scaling up ad spend.
What to do if the calculation gives you a budget you can't afford
If running this exercise shows the reasonable minimum budget for your sector is clearly above what your business can invest right now, the sensible options aren't "do it with less and hope for the best", but rethinking the strategy: focus the available budget on a smaller, more specific segment where cost per conversion is lower, invest first in improving the website's conversion rate (which lowers cost per sale without touching the media budget), or combine modest ad spend with SEO and content work, which over the medium term reduces total dependence on ad spend.
How to negotiate with an agency when the budget is tight
When the available budget is below what an agency considers its usual entry point, it's worth having an honest conversation instead of trying to force-fit into a service designed for bigger budgets. Some agencies offer reduced initial setup packages (properly building the account, measurement and a basic structure) with no ongoing monthly management commitment, letting the business itself maintain the campaign with occasional check-ins, a middle-ground option many small businesses with tight budgets don't know exists.
Another reasonable alternative is grouping the budget over time instead of spreading it month by month: instead of investing 200 euros every month for six months, concentrating 600 euros into two specific months of higher seasonal demand for the business, which can generate better results than diluting that same total amount into a constant trickle that never reaches the minimum volume the algorithm needs to learn well.
How seasonality affects the minimum viable budget
This article's reference figures assume relatively stable demand throughout the year, but many sectors have marked seasonality that makes the same budget perform very differently depending on the month. In high season, a budget that would be insufficient in low season can generate the minimum conversion volume needed thanks to higher natural demand, while that same budget in low season can fall short. Adjusting the minimum viable budget month by month, instead of setting a single figure for the whole year, usually delivers better results than maintaining constant spend that doesn't match real demand variations.
Comparing funding advertising from cash reserves versus credit
A question that comes up often at small businesses is whether it's better to wait until the minimum budget is saved up or to finance the initial campaign with some kind of credit, assuming the return will cover the financing cost. The reasonable answer depends on how much certainty exists about the outcome: if prior data already exists (a similar earlier campaign, a direct competitor with known results, a small-scale test already validated) that makes the return reasonably predictable, financing a campaign with credit can make sense, just like financing machinery purchases with a predictable return. If that degree of certainty doesn't exist and the campaign is purely experimental, it's more prudent to wait until the budget is available without needing financing, so as not to build up debt against an uncertain outcome.
Frequently asked questions
Is it better to start with a small budget and scale up, or wait until I have more and start strong?
It depends on the sector, but as a general rule it's preferable to start with the minimum budget that reaches the conversion volume the algorithm needs to learn (the ranges mentioned above), rather than spreading an insufficient budget over time hoping it "grows little by little", which usually generates fairly useless data for months.
Does the minimum budget include the cost of building the campaign, or just ad spend?
The figures above refer only to media spend (what you pay the platform). Initial setup, creatives and monthly management are an additional cost worth budgeting separately, and it varies a lot depending on whether the business does it in-house or hires an agency.
Can I split a small budget between Google Ads and Meta Ads at the same time?
With very tight budgets, that's usually not a good idea: it's better to concentrate the whole budget on the channel that best fits your sector (active search for urgent needs, social media for more visual or discovery-driven products) and only expand to a second channel once the first is already generating stable results.
How long should I maintain a minimum budget before deciding whether it works?
At least six to eight weeks, to give the campaign time to get past the learning phase and accumulate enough data. Judging performance in the first two weeks, especially with a tight budget, almost always leads to premature conclusions.
Are these figures the same across all of Spain or do they vary by region?
They vary, especially for local services: cost per click tends to be higher in Madrid and Barcelona, where there's more direct competition, and lower in mid-sized cities and areas with fewer businesses competing for the same keywords.
What if my sector has a much higher cost per click than average, like insurance or law?
In sectors with very high cost per click (often above 3-5 euros per click on the most competitive keywords), the reasonable minimum budget rises proportionally, and it often makes sense to complement paid search with SEO and content, which over the medium term reduces dependence on a cost per click that in those sectors keeps climbing.