Ad Budget Calculator
Size the ad budget your goal actually needs — and check it against your margin so you never buy unprofitable growth.
Written by Dorothy Ibrahim, 10+ years in banking & finance
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How we calculate this
This calculator sizes the ad budget a customer or revenue goal actually requires, then runs the check most budget math skips: whether you can afford each customer at that acquisition cost. It derives your cost per acquired customer (CAC) from cost-per-click and conversion rate (or takes your CAC directly), multiplies by the customers your goal implies, and compares the CAC against two affordability ceilings — what one order's gross margin covers, and what customer lifetime value justifies under the common 3:1 LTV-to-CAC convention.
The formulas
- Customer acquisition cost (CAC)
- cost per click ÷ conversion rateSkipped if you enter your CAC directly.
- Target customers (revenue goal)
- target revenue ÷ average order valueFor a customer-count goal, the target is used as entered.
- Required ad budget
- target customers × CAC
- Max profitable CAC (first order)
- average order value × gross marginSpend above this and each customer loses money on their first purchase.
- LTV-justified CAC (with repeat purchases)
- (average order value × gross margin × purchases per year) ÷ 3Uses the 3:1 LTV:CAC convention — a rule of thumb, not a lender or platform requirement.
Worked example
- Say your goal is 50 new customers, ads cost $1.50 per click, 2% of clicks convert, your average order is $100, gross margin is 45%, and customers buy once a year.
- CAC = $1.50 ÷ 0.02 = $75 per customer.
- Required ad budget = 50 × $75 = $3,750.
- Max profitable CAC = $100 × 0.45 = $45 — so at $75 you would lose $30 on every customer's first order.
- With one purchase per year, LTV = $100 × 0.45 × 1 = $45, and the LTV-justified CAC is $45 ÷ 3 = $15. A $75 CAC exceeds both ceilings, so the tool flags this budget as a no-go: the plan buys unprofitable growth unless conversion improves, CPC falls, or customers return more often.
Rates, benchmarks & sources
- The healthy LTV-to-CAC multiple of 3.0 used for the "LTV-justified CAC" ceiling. A widely used rule of thumb from SaaS and growth finance, not a regulation or lender standard. — Industry convention (3:1 LTV:CAC)
- CAC = CPC ÷ conversion rate; first-order breakeven CAC = AOV × gross margin; simple LTV = AOV × margin × purchase frequency. — Standard unit-economics definitions
Figures current as of 2026-07-02. See our methodology & editorial standards for how constants are versioned and verified.
What this tool doesn’t model
- Assumes CPC and conversion rate hold constant as spend scales. In real ad auctions, larger budgets usually mean higher CPCs and lower marginal conversion rates, so the budget shown is a floor, not a ceiling.
- Uses a deliberately simple LTV (order value × margin × yearly purchase frequency, one year). It ignores churn, multi-year retention, and discounting — a fuller LTV model can justify a different CAC in either direction.
- Results are only as good as your attribution: the conversion rate and any directly entered CAC assume you can correctly credit customers to your ads, and platform-reported conversions tend to flatter the platform.
- Ignores creative, agency, and management costs — the budget covers media spend only.
- The 3:1 LTV:CAC ceiling is a convention. Businesses with fast payback and strong cash positions sometimes accept more aggressive ratios; cash-tight businesses often need more conservative ones.
Frequently asked questions
How is my CAC calculated from CPC and conversion rate?
If 2% of clicks become customers, you need on average 50 clicks per customer, so CAC = CPC ÷ conversion rate — $1.50 ÷ 0.02 = $75 in the default example. This assumes the conversion rate is measured on the same clicks you are buying. If you already know your blended CAC from past campaigns, enter it directly instead; measured beats derived.
What does the go/no-go verdict actually compare?
Your CAC against two ceilings. "Go" means CAC is at or below your first-order margin (AOV × margin), so each customer is profitable on their first purchase. "Caution" means CAC exceeds first-order margin but fits within the LTV-justified ceiling — profitable only if customers really do come back. "No-go" means CAC exceeds both, and each customer costs more than they are worth under this model.
Why does the default example fail even though the budget seems small?
Because affordability is per customer, not total. A $3,750 budget is modest, but at a $75 CAC against a $45 first-order margin you lose $30 per customer — and spending more just scales the loss. The fix is in the inputs: a higher conversion rate or lower CPC cuts CAC directly, a higher order value or margin raises the ceiling, and genuine repeat purchases raise the LTV-justified limit.
Where does the 3:1 LTV-to-CAC rule come from, and do I have to follow it?
It is an industry convention, popularized in SaaS and growth finance, that a customer should be worth about three times what they cost to acquire — the buffer covers servicing costs, churn surprises, and the time it takes revenue to arrive. It is a rule of thumb, not a law or a lender requirement. The tool uses it as a sanity check; your own payback-period and cash constraints should set the final line.
Can I trust the conversion rate my ad platform reports?
Treat it with care — the budget this tool computes is only as good as that attribution. Ad platforms credit themselves for conversions inside generous attribution windows, including customers who might have bought anyway. Where possible, sanity-check platform numbers against your own order data (new customers ÷ ad clicks over the same period) before sizing a real budget on them.
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themoneysheet provides educational estimates, not financial, tax, or legal advice. Figures use published rates and formulas current as of the date shown, but your situation may differ. Consult a qualified professional (CPA, attorney, or licensed advisor) before making financial decisions.