ROAS, CAC and payback period: the marketing numbers that actually decide profit

Ad platforms love to show you ROAS. It is easy to read, it moves quickly, and it usually looks good. The trouble is that ROAS alone cannot tell you whether you are making money. Here are the numbers we use with clients to decide how much to spend and when to scale.

ROAS: useful, but incomplete

Return on ad spend is revenue divided by ad spend. If you spend ₹1,00,000 and the platform reports ₹4,00,000 in sales, ROAS is 4. That sounds strong, but it ignores everything between revenue and profit: product cost, shipping, returns, payment fees and discounts. A 4x ROAS on a product with a thin margin can still lose money.

Know your break-even ROAS

Break-even ROAS is one divided by your contribution margin. Contribution margin is the share of each sale left after the direct costs of fulfilling it.

• If your contribution margin is 50%, break-even ROAS is 2.
• If it is 25%, break-even ROAS is 4.

Anything above that line is profit on the first order. Anything below it is a loss on the first order, which may be fine if repeat purchases make up for it, but that should be a decision, not a surprise.

CAC: what a customer really costs

Customer acquisition cost is your marketing spend divided by the number of new customers it brought in. Two cautions:

1. Count new customers only. Platforms often credit conversions from people who already bought from you.
2. Include more than ad spend where you can: agency fees, creative production and tools. A blended CAC that includes everything is the number your finance team will recognise.

Payback period: how fast the money comes back

Payback period is how long it takes for a customer's gross profit to cover what you paid to acquire them. If you spend ₹800 to win a customer who earns you ₹400 in profit on the first order and ₹200 a month after that, you are paid back in about three months.

This number is what lets you be bold. A brand with strong repeat purchases can happily lose money on the first order, because the payback period is short and the lifetime value is high. A brand with few repeat buyers cannot, and needs to be profitable on the first order.

Why platform numbers and your numbers disagree

Google, Meta and your own analytics each use different attribution rules and windows, so they rarely match. Instead of arguing over which one is right, pick a single source of truth, usually your store or CRM data, and use the platforms for direction rather than accounting. Check the gap between them regularly. If it suddenly widens, something in your tracking has likely broken.

A simple monthly routine

1. Calculate contribution margin per product or category.
2. Work out break-even ROAS and target CAC from it.
3. Compare each channel's actual CAC with the target, using your own sales data.
4. Check payback period for your newest customer groups.
5. Move budget towards what beats the target and trim what does not.

The takeaway

Treat ROAS as a signal, and let margin, CAC and payback period make the decisions. They tell you not just whether campaigns are working, but whether the business is better off for running them.

If you would like these numbers worked out for your own account, our free audit includes the working so you can check it yourself. Clean tracking is part of our analytics work, and our performance marketing pages explain how we plan budgets.