How to use it

Start with today's numbers: impressions, CTR, average CPC and conversion rate, plus value per conversion and gross margin if you want revenue, ROAS and profit. Any period works, as long as every number covers the same one. If you know your monthly spend but not your impressions, choose Start from budget and the tree works back from the budget instead.

Every input in the tree then has a scenario value, which starts at your baseline. Move one with the stepper, the 10% buttons or by typing, and everything that depends on it updates, with the change beside each number: mint when it's better, red when it's worse, grey when it's neither. Spend is grey, because spending more isn't bad in itself. Use scenario as baseline locks a change in so you can stack the next one, and Reset scenario puts everything back.

For lead generation, the lead-gen stages carry conversions through qualified leads to customers, so you see cost per customer as well as CPA. What do I need to hit works backwards: pick a target, and it tells you what one number would have to be, with the rest held where they are. Copy summary gives you plain text for an email or Slack, and Copy table gives you rows for a spreadsheet.

The two numbers that set your CPA

CPA is cost divided by conversions. Cost is clicks times CPC, and conversions are clicks times conversion rate, so the clicks cancel out: CPA is CPC divided by conversion rate. At a £1.20 CPC and a 5% conversion rate, every conversion costs £24, whether you buy a hundred clicks or a hundred thousand.

That's why impressions and CTR, the numbers most reports lead with, aren't in it. They set volume. More impressions, or a better CTR on the same impressions, bring more clicks, more conversions and more spend in the same proportion, and CPA stays where it was. ROAS works the same way: it's conversion rate times value per conversion, divided by CPC. So when CPA moves, look at CPC and conversion rate first, and when volume moves, look at impressions and CTR.

Volume matters for profit. Each conversion earns its value times your margin, which is your break-even CPA: buy conversions below it and each one adds profit, buy them above it and each one loses money. Scale a profitable campaign and profit grows with it; scale an unprofitable one and so do the losses.

The tree uses only these identities, and it leaves some real effects out on purpose. In a live auction a better CTR can lower your CPC through Quality Score. Extra impressions usually come from less relevant searches or lower positions and convert a little worse, and a bigger budget tends to buy pricier clicks once the cheap ones are taken. Read a scenario as the arithmetic of a change, then allow for those.

What moves each number

Impressions

Budget, and the impression share you lose to budget or to ad rank. Keyword coverage: the keyword concatenation tool builds the combinations a list is missing. Match types, and the audience, location and ad schedule settings that widen or narrow the searches you're eligible for.

CTR

Ad relevance and assets: responsive search ad headlines that echo the search, and sitelinks and callouts that give the ad more room. The Ad Copy Battle puts your ad against rival angles before you pay for the clicks. Ad rank, since higher positions draw more of the clicks. Message match between the keyword and the ad. Negative keywords, which cut the impressions that were never going to click.

CPC

Quality Score, which Google Ads builds from expected CTR, ad relevance and landing page experience. Your bid strategy and its targets. How much competition there is in each auction. Match types and negatives, which decide which auctions you enter at all.

Conversion rate

Landing page speed, message match from the ad to the page, the offer itself, and friction in the form or checkout. For phone-led businesses, how calls are answered and handled. And measurement: the rate you see only counts what's tracked, and consent choices, blockers and journeys across devices all hide conversions.

Value and lead quality

Order value, through pricing, bundles and delivery thresholds. For lead generation, the quality of the leads and your close rate, which is where cost per customer is won or lost: in the signup engine case study, cost per signup more than halved while cost per customer fell by 15-20%.

Your numbers stay in your browser

The tree is plain JavaScript running in this page. It makes no network requests and sends your numbers nowhere, which matters when they're a client's. Nothing is saved unless you tick Remember my numbers on this device, which keeps them in this browser's local storage until you untick it.

If you've accepted analytics cookies, the site records which target you goal-seek, whether you copied the summary or the table, and which way in you chose, never a number. The privacy policy has the detail.