What is Cost Per Acquisition (CPA)?

CPA — sometimes used interchangeably with Customer Acquisition Cost (CAC) — is the total marketing and sales spend divided by the number of new paying customers gained. Formula: CPA = Total Spend / New Customers. A lower CPA means each customer costs less to win; combined with LTV it tells you whether growth is profitable.

How is Customer Lifetime Value (LTV) calculated?

For a subscription business the standard formula is LTV = ARPU x Gross Margin % / Monthly Churn Rate. For example, a product with $49 ARPU, 70% margin and 5% monthly churn has LTV = ($49 x 0.70) / 0.05 = $686. A one-time-purchase LTV uses average order value x purchase frequency x customer lifespan instead.

What is a healthy LTV:CAC ratio?

The widely-cited SaaS benchmark is 3:1 or higher — meaning each customer generates at least three times what it cost to acquire them. A ratio below 1:1 means you lose money on every customer at scale and must either reduce CPA or improve retention and monetisation before growing the channel.

What does ROAS mean, and how does it differ from ROI?

ROAS (Return on Ad Spend) = Campaign Revenue / Ad Spend. A ROAS of 3x means every $1 spent returns $3 in revenue — but revenue is not profit. ROI accounts for the cost of goods: ROI = (Revenue - Spend) / Spend x 100. You can have a positive ROAS and a negative ROI if your gross margins are thin.

What is CTR and why does it matter for CPA?

CTR (Click-Through Rate) = Clicks / Impressions x 100. A higher CTR means your creative is compelling enough to earn a click from a larger share of people who see it. CTR affects both the volume of traffic entering your funnel and your Quality Score in paid-search auctions, which lowers cost-per-click and therefore CPA downstream.

How do I reduce my CPA without cutting budget?

Four levers work independently: (1) improve ad creative and targeting to raise CTR; (2) improve landing-page relevance to raise conversion rate; (3) tighten audience segments to remove low-intent traffic; (4) run A/B tests on offers or pricing to lift conversion. Each moves the denominator (customers) up without touching the numerator (spend), driving CPA down.

Cost Per Acquisition (CPA) Calculator

Understanding exactly how much you pay to acquire each customer — and whether that cost is justified by what those customers are worth over their lifetime — is the single most important calculation in paid marketing. This Cost Per Acquisition (CPA) calculator combines eight metrics into one screen: CPA/CAC, customer LTV, the LTV:CAC ratio, ROAS, CTR, payback period, profit per customer and campaign ROI, plus a break-even analysis showing the minimum number of customers needed to cover fixed costs.

How it works

Fill in two sections. The Campaign & Spend section captures your ad spend, the number of new customers it produced, the revenue attributable to the campaign, total impressions served and total clicks received. The Unit Economics section captures the inputs needed to model lifetime value: monthly average revenue per user (ARPU), gross margin percentage and monthly churn rate. Optionally add your monthly fixed costs to unlock the break-even calculation.

Every metric is then computed in real time in your browser. No data is sent to any server.

The core formulas

CPA / CAC is the simplest: divide total ad spend by the number of new customers acquired.

LTV uses the standard subscription formula. First multiply your monthly ARPU by the gross margin percentage to get gross profit per user per month. Then divide by the monthly churn rate. Because 1 / churn equals the expected number of months a customer stays, you are effectively computing (monthly gross profit) x (expected tenure in months). A product with $49 ARPU, 70% gross margin and 5% monthly churn has LTV = (49 x 0.70) / 0.05 = $686.

ROAS = campaign revenue / ad spend. A ROAS of 3x returns $3 for every $1 spent.

CTR = clicks / impressions x 100. A 2% CTR means 2 out of every 100 people who see the ad click it.

Payback period = CPA / (ARPU x gross margin). This is how many months of gross profit are needed to recover the acquisition cost. A payback of 12 months is generally acceptable; under 6 months is excellent for most B2C subscription businesses.

LTV:CAC ratio = LTV / CPA. The industry standard benchmark for sustainable growth is ≥ 3:1.

Worked example

Suppose you run a $5,000 Google Ads campaign that generates 100 new customers and $15,000 in tracked revenue, served to 200,000 people who produced 4,000 clicks. Your product charges $49/month with 70% gross margin and 5% monthly churn, and you have $2,000 in monthly fixed costs.

Metric	Calculation	Result
CPA	$5,000 / 100	$50
LTV	($49 x 0.70) / 0.05	$686
LTV:CAC	$686 / $50	13.7x
ROAS	$15,000 / $5,000	3x
CTR	4,000 / 200,000	2%
Payback	$50 / ($49 x 0.70)	1.5 months
ROI	($15,000 - $5,000) / $5,000	200%

With LTV:CAC of 13.7x this campaign is exceptional. You break even on fixed costs after acquiring just 3 customers (3 x $636 profit = $1,908, covering $2,000 roughly). The tool calculates this exact threshold dynamically.

Formula note

The LTV formula above assumes a constant monthly churn rate and constant ARPU — a reasonable approximation for most SaaS and subscription products. For e-commerce or one-off-purchase businesses, substitute LTV = average order value x average purchase frequency x expected customer lifespan (in months or years). The CPA formula is universal: it works for any acquisition channel, any business model and any currency — just keep spend and revenue in the same unit.