Every bid change you make is a bet. **You might be right and improve the campaign, or wrong and make it worse** — and no amount of care removes that.

**So the goal is not to be certain. It is to place as many high-probability bets as possible, and to size each one against what it would cost to be wrong.**

Read this before your first few optimisation rounds. It is the mindset the bid, placement, bleeder and harvesting rules all sit on top of.

[Watch the walkthrough](https://kb.trackiq.com/kb-assets/kbvideo-calcbets-explainer-1b078f07.mp4)

*Prefer to watch? One hundred and fifty-two seconds on sizing a change to the cost of being wrong, steering campaigns toward target ACOS, and leaving the sweet-spot campaigns alone.*

## **The core rule**

**If a change has a high chance of helping, make it — even if it is small.** A 3% keyword bid rise in the right place compounds across months.

**If it has a low chance of helping, either skip it or shrink it.** Not 7% on the keyword — 3%. Not 25% on the placement — 10%.

**And if it has a serious chance of backfiring, do not make it at all.**

**That is the whole discipline.** Small positive changes stack up. One large negative change on a major campaign undoes a quarter of them.

## **Size the change to the size of the campaign**

**Large, established campaigns are a car at 100 mph.** A sharp turn crashes it. Keep placement changes to **5–10%** and keyword bids to **3–5%**.

**Small campaigns are a car at 20 mph.** You can make sharp turns and even U-turns safely, because there is very little at stake.

| Campaign | Placement bid change | Keyword bid change |
|---|---|---|
| **Large / 80-20 campaigns** | **5–10%** | **3–5%** |
| **Mid-size** | 10–15% | 5–7% |
| **Small / new** | larger changes are fine | larger changes are fine |

**The asymmetry is the point.** On your biggest campaign, being wrong is expensive and being right is only slightly better than doing nothing. On a small one, being wrong costs almost nothing.

## **Steering, not solving**

**Optimisation is not a maths problem with a correct answer.** Treating it as one is the most common reason people's changes backfire.

**Think of each campaign as a ship on a course**, where the course is your target ACOS.

**On course** — 30-day and 7-day ACOS both sitting near target. **Do nothing.** It is sailing correctly.

**Well below target** — say 20% against a 35% target. That is a promising campaign, not a finished one. **Raise bids and placement adjustments gradually** and let ACOS drift up toward target while spend grows. You are buying more volume at a price you can afford.

**Above target** — 39%, 43%, 47%. **Correct downward, gradually, over two to four weeks.**

**And let the gap set the aggression.** A campaign at 39% against a 35% target needs a nudge. One at 55% needs real correction.

![Campaign ACOS against target, at a glance](/kb-assets/shot-adv-campaigns-view-77ace2.png)

**Reading the gap between each campaign's ACOS and its target across a whole portfolio is the input to every decision here** — see [**Campaigns: Budgets, Placement and Audience Adjustments**](https://kb.trackiq.com/hc/knowledge-base/articles/advertising-campaigns). Rebuilding that view by exporting reports and pivoting them each week is hours of assembly before you have made a single decision.

## **Nurture the young, leave the mature alone**

A keyword or campaign that launched recently and immediately produced **low ACOS and strong conversion** is a young player with obvious potential.

**Invest in it.** Raise bids, raise placement adjustments, give it budget, and give it attention. You are trying to turn it into one of your main campaigns.

A campaign that has run for weeks or months at an ACOS you are happy with is at its peak.

**Leave it alone.** Frequent tweaking of something already performing has more downside than upside — the realistic outcomes are *unchanged* or *worse*.

### **The bands, against a 35% breakeven**

**ACOS 15–24%** — exceptional. **Push it.** Grow spend deliberately and let ACOS rise toward the high twenties.

**ACOS 25–33%** — the sweet spot. **Stop optimising and let it run.** A campaign spending $150 a day at 28% is worth far more than the same campaign spending $50 a day at 20%.

**ACOS at or above target** — correct it, at the pace the gap justifies.

**Over-optimising a campaign in the sweet spot is how you push it to 40%.** Which is no longer excellent — merely acceptable.

## **When one backfires**

**It will happen. Not if, when.**

**Document changes on your biggest campaigns** — the ones carrying a meaningful share of account spend. A short log of what you changed and when.

**Watch those campaigns for the following few days.** A big campaign going from 30% to 39% shows up quickly.

**When it does, undo the change.** The campaign and ad group history in the console shows exactly what you did.

**Then check it daily until it recovers.** Put the bids, placement adjustments and keywords back where they were when it was working. Re-enable what you paused; remove what you added.

**Do not panic, and do not compound it with a second correction.** Most campaigns recover fully.

## **Common mistakes**

**Treating optimisation as arithmetic**, and expecting a formula to produce the right bid.

**Making large changes to large campaigns**, where the downside dwarfs the upside.

**Optimising campaigns that are already in the sweet spot**, and pushing them out of it.

**Making every change the same size**, regardless of confidence or campaign size.

**Not documenting changes on major campaigns**, so you cannot undo what you cannot remember.

**Panicking after a backfire** and making a second aggressive change on top of the first.

## **Related**

- [**Bid Optimisation: Six Rules**](https://kb.trackiq.com/hc/knowledge-base/articles/bid-optimisation-six-rules) — the rules this mindset governs.
- [**Placement Bid Optimisation**](https://kb.trackiq.com/hc/knowledge-base/articles/placement-bid-optimisation) — the same logic applied to placements.
- [**Setting Target TACOS per Product**](https://kb.trackiq.com/hc/knowledge-base/articles/setting-target-tacos-per-product) — where the target you steer toward comes from.