If your costs spiked with dynamic bidding, it’s likely because Amazon is aggressively adjusting your bids in real time, especially with “Dynamic – up and down” enabled.
Switching to fixed bids can help stabilize spend and give you more control, but it may reduce visibility if your bids aren't competitive.
What You Can Do:
Try “Dynamic – down only” first — it lowers bids when conversion likelihood drops, but won’t raise them.
Test fixed bidding with a smaller budget to compare performance side-by-side.
Monitor your search term report — high CPCs may be from expensive, low-converting queries.
Pro Tip:
Start with fixed bids or “dynamic down only” when launching, then scale to “up and down” once you’ve identified strong-performing keywords.
