A bid adjustment is a percentage you add to or take off your bids when an auction meets a particular condition. You might bid 20% more for searches from people within your delivery area, or 30% less on tablets, so that your spending follows where your customers actually convert. Some advertisers and other platforms call it a bid modifier.
How bid adjustments work
You set adjustments at campaign or ad group level for several dimensions: device, location, ad schedule (day and time), audience segments and demographics such as age. Most take a value from a 90% decrease up to a 900% increase. Setting -100% on a device type stops ads showing on it entirely. To stop ads in a place or at a time, you exclude the location or leave that slot out of the schedule instead.
When several adjustments apply to the same auction, they multiply rather than add. Take a £2.00 bid with +20% for mobile and +10% for Greater London. The bid becomes £2.00 × 1.2 × 1.1, which is £2.64, not the £2.60 you would get by adding the percentages. Add a third adjustment and the effect compounds again, which is how bids drift far higher than anyone intended.
Adjustments behave differently with automated bidding. Smart Bidding strategies set bids at every auction using device, location, time and audience signals already, so they ignore most manual adjustments. The main exception is a -100% device adjustment, which still excludes that device. The detail varies by strategy and changes over time, so check Google’s current help page for the strategy you use.
Why it matters
With manual CPC bidding, adjustments are the main way to stop paying the same for very different clicks. A Leeds removals firm might find calls from mobile searchers at 8am convert at twice the rate of desktop visits at midnight. Without adjustments, both cost the same.
Understanding them also prevents false comfort. Many accounts move to Smart Bidding but keep a page full of old adjustments, and owners assume they are still shaping spend. Mostly, they are not. Clearing them out, or at least noting which still apply, saves the next person who works on the account from drawing the wrong conclusions.
Common mistakes
- Adding percentages in your head when they actually multiply.
- Setting adjustments from a handful of conversions, which is usually noise rather than a pattern.
- Keeping old adjustments on Smart Bidding campaigns and believing they still work.
- Using a -100% adjustment on mobile without realising how much search traffic happens on phones.
- Adjusting by location within a narrow radius, when location reporting is approximate at small scales.
How to act on it
If you use manual bidding, open the device, location, ad schedule and audience reports for the last 60 to 90 days. Compare cost per conversion for each segment with the campaign average. Where a segment is clearly and consistently better or worse, set a modest adjustment, around 10 to 20%, and review a month later before going further. Record the figures behind each adjustment, so the next review starts from evidence rather than memory.
If you use Smart Bidding, tidy away adjustments that no longer do anything so the account reflects reality, and keep only deliberate exclusions. If you are unsure which approach suits your account, I can look at it as part of setting up or reviewing Google search campaigns.