Before you borrow to scale ads, measure the margin

Borrowing to scale ads is a bet that the next euro of spend earns back more than it costs. Your dashboard shows the average euro. Sales-based financing is repaid out of every sale, including the ones your ads did not cause.

Money for growth runs through recent ecommerce videos. A dropshipping tutorial presents supplier credit and pay-later financing as the answer to not having starting capital (video). Another walks through the capital a new store needs and when payouts arrive (video). Under both sits the question every scaling brand meets: is the extra spend worth borrowing for?

Three numbers that do not line up

Take Shopify Capital as one example of sales-based financing. Shopify's own page describes repayment as "a fixed percentage of your store's daily sales, but only on days you make sales."

Put that next to the two numbers your decision depends on.

Only the middle row pays the loan back with profit, and it is the one number that is not on any screen.

Why the average overstates the next euro

The first budget reaches the buyers easiest to convert. Each step up reaches people a little less likely to buy, and platform ROAS averages all of them together, so it can hold steady while the return on the last euro falls. What a budget ladder does to incremental ROAS walks through that pattern, and the diminishing returns math shows why the average hides it.

A loan makes the gap expensive. Spend that earns less than it costs is a loss either way. Borrowed spend is that loss plus a fee, repaid from sales you would have made anyway.

The lender is paid on your revenue and the ad platform on your spend. Neither is paid on your profit, so neither's numbers were built to tell you whether the loan pays.

The arithmetic, with your own numbers

What to pull:

1. The total extra spend the loan would fund.
2. Your contribution margin rate: what is left of a euro of revenue after product cost, shipping, payment fees and returns. POAS vs ROAS and returns-adjusted ROAS cover the parts people forget.
3. The total cost of the money: the fee, and how fast repayment comes out of sales.
4. The incremental revenue the extra spend would bring, from a test rather than from the dashboard.

The line to clear, in words: incremental revenue times your contribution margin rate has to cover the extra spend plus the financing fee. Divide both sides by the extra spend and you get the incremental ROAS the extra budget must reach: one plus the fee as a share of the extra spend, divided by your margin rate.

Compare that with what a test shows, not with reported ROAS. If reported ROAS clears the line and the tested return does not, the loan would be paying for sales you already had. The break-even ROAS calculator covers the margin side, and there are more free tools at /tools.

Timing matters as well. Sales-based repayment is taken from sales as they come in. If part of your revenue arrives later as marketplace payouts, or leaves again as refunds, it runs on a different schedule from the repayment. Map the weeks before you sign, so a strong month on paper does not become a tight month in the bank.

Red flags before you sign

Four signs the loan is being judged on the wrong number:

1. The case quotes reported ROAS. If the argument for borrowing rests on the platform's own return figure, it rests on the average of past spend, including sales that would have happened anyway.
2. The extra budget goes to retargeting or branded search. Those campaigns are the most exposed to claiming sales that were already on their way, so test them first. Is your branded search actually incremental? shows how.
3. There is no test period. Borrowing before a step-up test means the first honest reading of the extra spend arrives together with the first repayment.
4. The case is built on peak weeks. A return measured in a strong season may not hold in the weeks after it, so a plan sized on the peak can commit spend that the quieter months will not carry.

How to get the incremental number before you borrow

Two designs you can run on your current budget:

1. A regional step-up. Raise spend in some regions and hold the rest at today's level for the same weeks, then compare total orders between the two groups, not the orders each platform claims. Geo-lift testing for ecommerce covers the setup. Divide the extra orders by the extra spend and you have a number the loan can be judged against.
2. A time-boxed step-up. If regions are not an option, raise spend for a fixed number of weeks and then return to the old level, comparing total orders with the weeks before and after. It is weaker, because anything else that changed in those weeks lands in the result, but it costs nothing except discipline.

Rule of thumb: if the step-up cannot show a difference in total orders, do not borrow against the dashboard's number. What budget decisions on reported ROAS alone cost is the long version of why.

Where a read fits

Then, for a second opinion on which channel should get the extra budget, a causal attribution read such as Causality Engine's reads your GA4 Attribution paths export and shows what each channel caused next to what last-click gave it, with a next step for every channel. It is €99 once per upload, excluding VAT, with a full refund within 30 days, no questions asked.

Related answers

• What a budget ladder does to incremental ROAS
• What budget decisions on reported ROAS alone cost
• POAS vs ROAS: why profit on ad spend changes how you scale
• Geo-lift testing for ecommerce
• A viral post makes your paid ROAS look better