LTV, CAC, and the ratio that defines unit economics
The LTV:CAC ratio is the single most important unit economics metric for subscription and recurring revenue businesses. It answers the fundamental question: for every dollar spent acquiring a customer, how many dollars does that customer generate in gross profit over their lifetime? A ratio of 3:1 means each dollar of acquisition cost produces $3 of gross profit. A ratio below 1:1 means the business loses money on every customer it acquires, regardless of revenue growth.
LTV (Customer Lifetime Value) is the total gross profit generated by one customer from the moment of acquisition until churn. It is always calculated on gross profit, not revenue, because revenue before COGS overstates the economic value. A SaaS business with 80% gross margin and $100/month ARPU generates $80/month in gross profit per customer. With 2% monthly churn (50 months average lifetime), LTV = $80 × 50 = $4,000. CAC (Customer Acquisition Cost) is the total sales and marketing spend divided by the number of new customers acquired in the same period.
The formulas
LTV = (ARPU × Gross margin) ÷ Monthly churn rate
LTV = Monthly gross profit per customer × Average customer lifetime
Average customer lifetime (months) = 1 ÷ monthly churn rate
CAC = Total S&M spend ÷ New customers acquired
LTV:CAC ratio = LTV ÷ CAC
CAC payback period (months) = CAC ÷ (ARPU × gross margin)
Discounted LTV = ∑ [Monthly GP × (1 + discount rate)^(-t)] for t = 1 to lifetime
CAC payback (revenue basis) = CAC ÷ ARPU
LTV should always use gross profit margin, not revenue, because COGS is a real cash cost. The discounted LTV applies a monthly discount rate (annual rate / 12) to each future month of gross profit, reflecting the time value of money. Investors increasingly prefer discounted LTV for longer-lifetime businesses.
LTV:CAC benchmarks by business type
| Business type | Typical LTV:CAC | Typical payback | Churn range | Key driver |
|---|
| B2B SaaS (SMB) | 3x – 5x | 12 – 18 mo | 1% – 3%/mo | Retention and expansion revenue |
| B2B SaaS (Enterprise) | 5x – 10x | 18 – 24 mo | 0.5% – 1.5%/mo | Contract size and stickiness |
| B2C subscription | 2x – 4x | 6 – 12 mo | 3% – 8%/mo | Activation and habit formation |
| E-commerce / D2C | 2x – 5x | 3 – 9 mo | N/A (repurchase) | Repeat purchase rate and AOV |
| Marketplace | 3x – 8x | 6 – 18 mo | 2% – 5%/mo | Network effects and take rate |
Improving LTV:CAC
There are four independent levers: reduce churn (longest-lasting impact because it extends lifetime and compounds), increase ARPU through upsells, expansion revenue, or price increases, improve gross margin which directly multiplies every dollar of revenue into more LTV, and reduce CAC by improving conversion rates, shifting to lower-cost channels, or increasing organic acquisition. Of these, churn reduction is typically the highest-impact lever because its effect on LTV is multiplicative: halving churn from 4% to 2% doubles average lifetime from 25 months to 50 months, doubling LTV without any change to pricing or margin.
Worked examples
Example 1: B2B SaaS, SMB segment
ARPU: $200/month. Gross margin: 78%. Monthly gross profit per customer: $156. Monthly churn: 2%. Average lifetime: 1/0.02 = 50 months. LTV = $156 × 50 = $7,800. CAC = $2,600. LTV:CAC = 7,800/2,600 = 3.0x. Payback period (gross profit) = 2,600/156 = 16.7 months. This is within the acceptable SaaS range. To reach 5x LTV:CAC, either reduce CAC to $1,560, or reduce churn to 1.2% (LTV becomes $13,000).
Example 2: D2C e-commerce, repeat purchase model
Average order value: $60. Gross margin: 45%. Average purchases per year: 4. Annual gross profit per customer: $60 × 45% × 4 = $108. Average customer lifetime: 3 years. LTV = $108 × 3 = $324. CAC = $80. LTV:CAC = 324/80 = 4.05x. Monthly revenue payback = 80 / (60 × 4/12) = 80/20 = 4 months. Excellent for D2C.
Example 3: Impact of churn reduction
Starting scenario: ARPU $150, gross margin 70%, monthly churn 5%, CAC $1,000. Monthly GP = $105. Lifetime = 20 months. LTV = $2,100. LTV:CAC = 2.1x (marginal). If churn is reduced to 2.5%: lifetime = 40 months. LTV = $4,200. LTV:CAC = 4.2x (healthy). If churn is further reduced to 1.5%: lifetime = 67 months. LTV = $7,035. LTV:CAC = 7.0x (strong). The same ARPU and margin produced a 3.3x improvement in LTV:CAC purely from halving churn twice.
| Scenario | ARPU | GM | Churn | LTV | CAC | LTV:CAC | Payback |
|---|
| B2B SaaS (SMB) | $200 | 78% | 2%/mo | $7,800 | $2,600 | 3.0x | 17 mo |
| D2C e-commerce | $20/mo equiv. | 45% | N/A | $324 | $80 | 4.1x | 4 mo |
| High churn B2C | $30 | 60% | 8%/mo | $225 | $150 | 1.5x | 8 mo |
| Enterprise SaaS | $2,000 | 80% | 0.8%/mo | $200,000 | $25,000 | 8.0x | 16 mo |
Frequently Asked Questions
Should LTV be calculated on revenue or gross profit?+
LTV must be calculated on gross profit, not revenue. Using revenue overstates the economic value because COGS is a real cash cost that must be incurred to deliver the product or service. A business with $100 ARPU and 50% gross margin generates only $50 of value per month per customer, not $100. Calculating LTV on revenue would produce a 2x inflated figure. The gross-margin-adjusted LTV is the figure that correctly represents the cash generated to cover operating expenses, marketing, R&D, and eventually profit. Investors and acquirers always ask for gross-profit LTV, and any model using revenue LTV will be immediately rejected in due diligence.
What is the correct way to calculate CAC?+
CAC is total sales and marketing spend for a period divided by the number of new customers acquired in the same period. The definition of what to include in S&M spend varies. A conservative and investor-preferred definition includes: salaries and benefits of all sales and marketing staff, advertising and paid acquisition spend, agency and contractor fees, sales software and tools (CRM, marketing automation), trade show and event costs, and any other costs directly attributable to acquiring customers. It should not include customer success costs (which are retention, not acquisition) or product costs. Some founders use a blended CAC that includes both acquisition and onboarding costs, which is also legitimate as long as it is disclosed and applied consistently.
Why is LTV:CAC of 3:1 the SaaS benchmark?+
The 3:1 benchmark emerged from empirical observation of successful SaaS businesses and was popularised by David Skok and the SaaS Capital research community. At 3:1, the gross profit generated by a customer is three times the cost to acquire them, leaving approximately two-thirds of LTV to cover operating expenses, R&D, and generate a return. Ratios below 3:1 typically indicate that the business cannot generate sufficient margin to cover its other costs and reach profitability at scale. Ratios well above 3:1 (say, 8x to 10x) can indicate the business is under-investing in growth — leaving profitable acquisition opportunities unexploited. The optimal ratio varies by stage: early-stage companies often target 3x minimum, while later-stage companies may target higher ratios as they focus on profitability.
How does expansion revenue affect LTV?+
Expansion revenue (upsells, cross-sells, seat additions) increases ARPU over time and therefore increases LTV significantly. The basic LTV formula assumes a constant ARPU throughout the customer lifetime, which understates LTV for businesses with strong net revenue retention above 100%. For a business where ARPU grows at 10% per year (common in enterprise SaaS with expansion), the corrected LTV formula should use the expected average ARPU across the lifetime, not the initial ARPU. In practice, businesses with net revenue retention above 100% have theoretically infinite LTV if lifetime were infinite, which is why the discounted LTV formula is more appropriate for such businesses. The calculator uses a flat ARPU assumption; adjust the ARPU input to reflect the expected average rather than the initial value to account for expansion.
What is a good CAC payback period?+
Payback period should always be measured on a gross-profit basis (CAC divided by monthly gross profit per customer), not on a revenue basis. For VC-backed SaaS companies, a payback period under 12 months is considered excellent and under 18 months is good. Payback periods above 24 months are increasingly scrutinised by investors, particularly post-2021, as the focus shifted from growth at all costs to capital efficiency. E-commerce and D2C businesses typically require much shorter payback periods (3 to 9 months) because they lack the predictable recurring revenue of SaaS. Enterprise SaaS companies can justify longer payback periods (18 to 36 months) because contracts are larger, churn is lower, and switching costs create more durable revenue streams.
What is discounted LTV and when should I use it?+
Discounted LTV (dLTV) applies a discount rate to each future month of gross profit to reflect the time value of money: a dollar received in three years is worth less than a dollar received today. The standard LTV formula implicitly values all future cash flows equally regardless of when they arrive. For businesses with short customer lifetimes (under 24 months), the difference between standard and discounted LTV is small. For businesses with very long lifetimes (60+ months), the discount can be substantial. Discounted LTV is particularly important when comparing businesses with different lifetime profiles, when justifying a high multiple acquisition price, or when making capital allocation decisions in a high-interest-rate environment. A discount rate of 8% to 15% annually is typical, reflecting either cost of capital or the opportunity cost of deploying funds elsewhere.