What is a good marketing budget for ecommerce?

Usually, a good marketing budget is the most you can spend while the extra sales it causes still cover their cost at your margin. That makes it a ceiling you work out, not a percentage you copy. If you have no tests yet, start from your break-even point and raise the budget in steps you can measure.

The usual answer is a percentage of revenue, borrowed from a survey or a rule of thumb. It is easy to say in a meeting and easy to copy. It also gets cause and effect backwards. Revenue partly follows the budget, and the rule makes the budget follow revenue.

A budget has two jobs. It has to pay for itself at your margin, and it has to buy sales you would not get anyway. A percentage rule checks neither, which is why two stores with the same revenue can need very different budgets.

What one store's data shows

One store's anonymised GA4 export, 1 January 2024 to 21 August 2026. It holds shares of revenue only: no ad spend, no order counts.

The Break-even sheet holds arithmetic, not a result: at a 40% margin, break-even ROAS is 2.5x, because 1 divided by 0.40 is 2.5. That line is the spine of any budget. Spend that brings back less than that in sales it caused loses money, however good the dashboard looks.

Direct holds 57.7% of revenue in every view of that store's Channels sheet. A budget set as a share of revenue sizes itself on all of it, including whatever would arrive with every ad switched off. The rule pays marketing a commission on sales it may not have made.

One-touch journeys carry 79.5% of revenue in the store's Journeys sheet, at 0.5 days to buy. In the Journeys sheet, journeys with 4 to 9 touches hold 5.4% and took 16.9 days. Most of the money moves fast, and a slice moves slowly. Raise the budget in March and some of what it buys lands in April. Judge March alone and the new money looks lazier than it is.

What the export cannot show is spend. Without it there is no return to compute, so the export can't say how big that store's budget should be. It shows where credit sits and how fast buyers move, which tells you how to test a budget, not its size.

Why does a percentage of revenue mislead?

It ignores your margin. Two stores with equal revenue can have very different room for ads. For illustration, at a 60% margin break-even ROAS is about 1.7x; at a 25% margin it is 4x. The same percentage can be cautious for one store and ruinous for the other.

It ignores your stage. A new store buying its first customers may lose money on a first order and earn it back on the second. A mature store living on repeat orders mostly needs to stop paying for sales that come back on their own. One percentage can't serve both.

It funds credit, not cause. Budgets justified on platform-reported revenue pay for whatever the platforms counted. Brand search and retargeting collect buyers who were already coming, and the rule rewards them for it.

It hides the curve. The first euros in a channel reach the warmest buyers, and later euros reach colder ones. A flat percentage assumes every euro works equally hard, and they usually don't.

What does a good budget look like on paper?

Three numbers, in this order.

A ceiling from margin. For illustration, take €50,000 of monthly net sales and a 40% gross margin. If you want 10% of net sales left after product costs and ads, ads can take at most 30%, or €15,000. That is the most the month can carry, and only if the ads earned every sale. Some sales would have come anyway, so treat it as a limit, not a target.

A starting point under it. If your blended return, net sales divided by total ad spend, clears break-even with room, start from today's spend. If it doesn't, you are already over the ceiling.

A tested next step. Before raising the budget, buy the answer in a few regions. Google's geo guide describes a heavy-up test, run to confirm if additional dollars remain profitable. For illustration, if an extra €2,000 brings €6,000 of extra sales at a 40% margin, that is €2,400 of gross profit, so keep going. If the next €2,000 brings €4,000, that is €1,600 back for €2,000 spent, so stop there.

That is the whole method: a limit from margin, and steps checked by tests. Boring, cheap and hard to argue with.

What to do this week

1. Check your blended return against break-even. In Shopify admin, go to Analytics, then Reports, and open Total sales over time for last month. Divide net sales by total ad spend across all platforms. Pass: the result clears 1 divided by your gross margin with room to spare. Fail: it doesn't, so the budget is already too big for your margin, whatever the platforms report.
2. See whether spend bought new customers. In Shopify admin, open Analytics, then Reports, and filter the Category to Customers. Open New customers over time, grouped by month. Pass: new customers rose in the months spend rose. Fail: spend went up while new customers stayed flat, so the extra budget mostly bought orders you would have had.
3. Price your next step first. In Google Ads, click the Goals icon, open the Measurements drop-down and click Lift measurement. Or plan a heavy-up in a few regions. Pass: you have dates and regions for a test of extra budget. Fail: there are no clean weeks before your peak, so hold the budget flat until after it.

Check the homework. Your GA4 Attribution paths export already holds the evidence. Causality Engine reads that one file and shows what each channel caused next to what last-click gave it, in 1 to 2 minutes, for €99 once (excluding VAT), refundable within 30 days. Check the homework

Sources, 1 October 2026: Implement campaigns for geo experiments (Google Ads Help); Sales reports (Shopify Help Center); Customers reports (Shopify Help Center); Understand your Conversion Lift based on geography measurement data (Google Ads Help)

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