A 3× ROAS can be healthy for one business and a loss for another. What matters is how much of each order is left after product cost, taxes, fees, shipping and returns. That amount is the most you can spend on ads to win an order and still break even.
Enter your selling price including GST, the GST rate, product cost, payment or marketplace fee, shipping, packaging, other per-order costs and your return or RTO rate with the cost of each return. The calculator shows the contribution left per order, the break-even ROAS and CPA, and a target ROAS and CPA once you set the profit you want to keep as a share of the ex-GST price.
ROAS is calculated on the GST-inclusive price, which is how most ad platforms record purchase value when you send the order total; the ex-GST figure is shown too. Returned orders are assumed to bring the product back and refund the fee. Change the inputs if your returns work differently. The result is a planning number for one order, not a forecast of campaign results.