Most advertisers approach budgeting from one of two directions. The first is working backward from a goal: you know how many conversions you need and what you can afford to pay for each one, and you need to know how much budget that requires. The second is forecasting forward from a budget: finance has allocated a fixed monthly spend, and you need to estimate how many clicks and conversions that will realistically produce.
This calculator supports both directions. The math is the same underlying relationship between budget, cost-per-click, conversion rate, and cost-per-acquisition — it's just solved for a different variable depending on which number you already know.
In Google Ads, under Campaigns, the Avg. CPC and Conv. rate columns show your historical performance. If you don't have running campaigns yet, the Keyword Planner tool inside Google Ads gives CPC estimates by keyword and industry.
Forecasts assume your CPC and conversion rate stay constant, but both fluctuate with competition, seasonality, and ad quality. Treat this as a planning estimate and revisit it monthly with updated real numbers.
Google Ads allows daily spend to exceed your daily budget on high-traffic days (up to roughly double), balanced out over the month — dividing by 30.4 (the average days per month) is a more accurate daily target than dividing by exactly 30.
The underlying budget math applies to any CPC-based campaign type, though Performance Max in particular can have more variable CPCs across its automated placements, so treat the output as a starting estimate rather than a guarantee.