Switching to POAS Bidding in Google Ads: The Practical Guide (Stop Chasing Revenue)

Why Revenue Is Lying to You

There’s a version of Google Ads success that looks brilliant on paper and ruins your business in practice. Strong revenue numbers, healthy-looking ROAS, a dashboard full of green — and a bank account that tells a completely different story.

The problem is structural. ROAS treats all revenue as equal. It does not know that your £100 sale cost you £90 to fulfil, or that your £50 sale cost you £10. It sees two sales and calls both wins.

Here’s the same scenario made concrete:

Product A: Sells for £100, costs £90 to fulfil. Margin: £10. You spend £20 on ads to generate that sale. ROAS = 500%. Actual result: you lost £10.

Product B: Sells for £50, costs £10 to fulfil. Margin: £40. Same £20 ad spend. ROAS = 250%. Actual result: you made £20 profit.

Product B’s ROAS looks worse. Product B is the one keeping the lights on. ROAS cannot tell the difference — and that is why so many ecommerce businesses are scaling the wrong products.

Your Break-Even ROAS by Profit Margin

• 10% margin — requires 10.0× ROAS (1,000%) just to break even
• 20% margin — requires 5.0× ROAS (500%) just to break even
• 30% margin — requires 3.33× ROAS (333%) just to break even
• 40% margin — requires 2.5× ROAS (250%) just to break even
• 50% margin — requires 2.0× ROAS (200%) just to break even
• 70% margin — requires 1.43× ROAS (143%) just to break even

What POAS Actually Is (The Trojan Horse Method)

Google Ads does not have a POAS bidding button. What it does have is Target ROAS — and you can use that infrastructure to optimise for profit instead of revenue by changing what you report as the conversion value.

Instead of telling Google an order was worth £100, you tell it the order was worth £40 (after subtracting £60 in costs). Google’s bidding algorithm still runs Target ROAS. It just thinks ROAS means profit on ad spend now, because that is what the conversion values represent.

This is the whole method. You are not building new bidding infrastructure. You are changing the number you feed into existing infrastructure so it optimises for the right thing.

Implementing POAS: The Automated Path (Recommended)

1. Choose your profit tracking toolThree tools do this job well: ProfitMetrics (straightforward, does exactly what it says), Reaktion (stronger on data visualisation), and Pixel Manager for WooCommerce (the best option if you’re on WooCommerce). All three connect to your store and pass profit values to Google automatically.
2. Enter your Cost of Goods Sold for every productThis is the hard part — and the most important part. For every product, enter the cost to you: product cost, packaging, any per-unit fulfilment cost. If you skip this or use rough estimates, the tool assumes 100% margin and bids far too high. Take your time here.
3. Let the tool create a new conversion actionOnce connected, the tool creates a new conversion in Google Ads — typically called ‘POAS’ or ‘Gross Profit’. This is the conversion you will eventually make primary. Do not touch or delete your existing revenue conversion yet.

Implementing POAS: The Manual DIY Path

1. Capture the Google Click ID (GCLID)Shopify: Edit your theme.liquid to save the GCLID in a cookie, then pass it through as a cart attribute so it appears on every order export. WooCommerce: Install the ‘HandL UTM Grabber’ plugin, which captures the GCLID automatically and attaches it to orders.
2. Track your cost of goodsShopify: You can store product costs natively in Shopify admin under each product variant. WooCommerce: Install the ‘Cost of Goods for WooCommerce’ plugin to add a cost field to every product.
3. Export, calculate, uploadExport your orders to CSV. Add a Profit column: Revenue − Cost − Shipping = Profit. Upload the file to Google Ads via the Conversions section, mapping your Profit column to ‘Conversion Value’. Do this on a regular schedule — weekly works for most stores.

The Overhead Gotcha (Get This Wrong and You'll Overbid)

Here is where most people stumble: they try to account for rent, wages, software subscriptions, and other fixed overheads inside the conversion value they send to Google. Do not do this.

Your fixed overheads exist whether you sell one unit or a thousand. Your Google Ads bid should not change based on costs that are unaffected by volume. Subtract fixed costs from your conversion values and you will underbid on every order.

What to send Google: Gross profit — Revenue minus Cost of Goods and direct fulfilment costs like shipping. This is the contribution margin: the money available to cover your fixed costs and, beyond that, generate actual profit.

How to account for fixed costs: Adjust your Target POAS instead. If fixed costs consume roughly 30% of your gross profit, you need a POAS of at least 1 ÷ (1 − 0.30) = 1.43, or 143%, just to break even. Set your target above that to generate real profit.

The Safe Switch Protocol: Three Phases Over Four Weeks

1. Phase 1 — Observation (Weeks 1–3)Add your profit conversion action as a secondary conversion in Google Ads. Do not change your bidding strategy. Let both conversions run in parallel. After two to three weeks, compare the profit values being reported against your actual backend numbers. If they match, you are ready to proceed.
2. Phase 2 — The Flip (Week 4)Make your profit conversion the primary conversion. Demote your revenue conversion to secondary. Your bidding strategy remains Target ROAS — nothing changes there. What changes is the value Google is now optimising for.
3. Phase 3 — Reset Your Target (Critical Step)Do not carry your old ROAS target across. Pull your historical data for the previous month and calculate your actual POAS during that period. If it was 150%, set your new target at 150%. If you leave the old target at 400%, Google will try to achieve £4 of profit for every £1 spent — almost certainly impossible — and your ads will stop spending entirely.