If your ad metrics are stable but cost per purchase is rising, check the cart to checkout rate. A drop at that single step usually means a website problem (cart drawer, surprise shipping cost, app conflicts or a checkout button below the fold), not an ad problem.
Here's a pattern we see often. Cost per purchase climbs. The team pauses ads, swaps creative and changes budgets. Nothing helps, because nothing in the ads changed. Click-through rate, cost per click and add-to-cart rate all held. What changed was the share of carts that reached checkout.
How to spot it
Pull four numbers by week from Meta or GA4: landing page views, adds to cart, checkouts started and purchases. Then calculate the rate between each step.
| Step | Healthy range | If it drops |
|---|---|---|
| Landing page to cart | 8 to 15% of sessions, higher on paid social | Product page, price or offer issue |
| Cart to checkout | 40 to 60% | Cart drawer, shipping surprise, technical issue |
| Checkout to purchase | 55 to 75% | Payment options, trust, unexpected costs |
If ads and landing page to cart hold steady but cart to checkout falls, stop changing the ads. The leak is on the site.
The usual causes
- Layout shift in the cart drawer that moves the checkout button as it loads
- A shipping cost that only appears in the cart
- Apps that add scripts, upsells or pop-ups between cart and checkout
- A checkout button below the fold on mobile
- Broken express payment buttons
What to do
- Test your own cart on a real phone, on mobile data.
- Check the browser console on the cart and checkout pages for errors.
- Fix the cart before you touch the ads.
Our Product Page CRO Checklist covers the full list.
Growth bottleneck audit
Frequently asked questions
What is a good cart to checkout rate?
Many stores see 40 to 60% of carts reach checkout. A sudden drop from your own normal level matters more than any benchmark.
How do I find cart to checkout rate?
Divide checkouts started by adds to cart, using Shopify analytics, GA4 or Meta pixel events for the same period.
Written by Shimeez Bok, founder of Growth Alchemy, an ecommerce growth studio in Auckland, New Zealand.
