Work backward from the business goal to the media budget and performance assumptions required to reach it.
A useful marketing forecast exposes the assumptions between budget and outcome. It should show the expected CPC or CPM, conversion rate, CPA, AOV or ROAS rather than simply declaring a revenue target.
Build ranges, not false precision. Auction cost, conversion rate and marginal efficiency can change as spend expands, so low/base/high scenarios are usually more informative than one exact number.
Each tool answers a different part of the same operating question.
A business wants $100,000 in attributed revenue at a 4.0x target ROAS. The simple budget implication is $25,000. If AOV is $100, that implies about 1,000 orders. At a 2% conversion rate, roughly 50,000 relevant visits are required.
Illustrative only. Replace every input with your own business data before making a decision.
Every forecast should be traceable from outcome to traffic.
Choose revenue, customers or contribution.
Target ROAS and maximum CPA.
Orders, conversions, clicks and traffic.
Create conservative, base and growth scenarios.
CPA may rise as budget expands.
That leaves no contribution buffer.
A forecast should show the rates behind the headline output.