A budget calculator that does not flatter.
Ordinary calculators multiply budget by conversion rate and get linear growth. That does not exist in advertising: as you spend more, clicks get dearer and the conversion rate falls, because you are reaching less certain searches. This calculator accounts for that, and instead of one pleasant number it shows you the three that actually decide a budget: marginal CPA, profit optimum & break-even.
Pick an industry, replace the values with real numbers from your account and move the budget. The defaults are a starting position, not a market benchmark.
The model peaks at around €2,413 and you are at €2,700. Further profit will not come from budget now, but from a better conversion rate, margin or lower CPC.
| Budget | Conversions | Marginal CPA | Profit from step | Gross profit total |
|---|---|---|---|---|
| €405 | 29 | €14 | €583 | €583 |
| €810 | 47 | €22 | €212 | €796 |
| €1,215 | 63 | €26 | €122 | €917 |
| €1,620 | 77 | €29 | €71 | €988 |
| €2,025 | 90 | €31 | €36 | €1,024 |
| €2,430 | 102 | €33 | €10 | €1,034 |
| €2,835 | 113 | €35 | −€10 | €1,024 |
| €3,240 | 125 | €36 | −€27 | €997 |
| €3,645 | 135 | €38 | −€41 | €956 |
| €4,050 | 146 | €39 | −€53 | €903 |
Want to know whether this holds for your account? We will go through your real numbers and say where the next unit would earn.
I want an account reviewHow we calculate it and what the model cannot do. We model conversions with a power-law advertising response, K(S) = A · S^e. The exponent e expresses market saturation: as budget grows the click gets dearer and the conversion rate worsens, because you are reaching less certain searches. From that follows the key figure of the whole calculator: marginal CPA = average CPA ÷ e. At e = 0.7 the last conversion added is therefore about 43 % dearer than the account average. The profit optimum is the point where the gross margin from a marginal conversion equals one unit spent. The model does not know your competitors, your season, your stock capacity or the learning phase of automated bidding, and it does not account for returns, repeat purchases or management fees. It is a frame for a decision, not a forecast. The real response of your account will only show in a controlled budget test or a geo experiment. The industry defaults are our estimates for that market, not measured data — which is why every number is editable and the result will be far more useful with yours.
Common
budget questions.
These are what we get asked most. The answers are the longer version of what the calculator does above the chart.
How do I work out a PPC budget?
Backwards, from margin. Work out the gross margin on one order or job — that is the absolute ceiling on what you can pay to win it. Then take your real CPC and conversion rate from the account and work out how many clicks you need. The budget that comes out does not hold linearly though: as you spend more, the click gets dearer and the conversion rate falls, so the last conversion added costs more than the account average.
Why does doubling the budget not double the orders?
Because the first units of spend go to the cheapest and most willing customers: people searching for your brand or a specific product. Every further unit goes into dearer auctions and less certain searches. The return on added money is therefore almost always worse than the account average. In the model this is the saturation exponent: at 0.7, doubling the budget gives about 62 % more conversions, not 100 %.
What is marginal CPA and why does it matter more than the average?
Marginal CPA is the cost of the conversion brought by the last unit of budget — not the average across the account. With a power-law advertising response, marginal CPA equals average CPA divided by the saturation exponent. At e = 0.7 it is therefore about 1.43× higher. That is exactly why an account can be profitable overall while the added budget loses money: the decision to add or not is governed by the marginal figure, never the average.
How accurate is the calculator?
It is a model, not a forecast, and we say so plainly. It gives the right frame for a decision and the right questions, but it does not know your competitors, your season, your capacity, your returns or the learning phase of automated bidding. The industry defaults are our estimates for that market, not measured data. The more of them you replace with real numbers from your account, the more useful the result. The real response of a budget only shows in a controlled test or a geo experiment.
Does the budget include management fees?
Not in this calculator. We model only the media budget, that is money flowing into the ad platforms. Add management fees, creative production and work on the site separately. At small budgets they are a substantial part of total cost and they lower the calculated optimum, because the fixed cost also has to be paid out of margin.
Read alongside it
The calculator gives a number. These three articles explain why that one.
PPC budget: why double the money never doubles the orders
The number that decides a budget is not average cost per conversion but marginal — the cost of the conversion the last unit of spend brings. It is always higher, it can be calculated, and it changes everything.
Article library →ROAS, CPA, CAC and LTV: which number actually decides
Most arguments about PPC results are arguments about the metric, not the performance. A ROAS of 6 can be a win or a loss. Here is the converter between all of them, the ceiling each implies from your margin, and one table you can rewrite with your own number.
Article library →Incrementality: how to find out what advertising actually brought
Attribution says who to credit a conversion to. Incrementality says whether it would have happened at all. It is the one question you cannot answer from an ad platform interface — and at larger budgets the most important one.
Article library →Want it
on your own data?
We will send you the calculation on your real account numbers, not our industry estimates. Free and with no obligation to work with us.