SaaS Unit Economics Deep Dive: LTV, CAC, and Payback Mastery

Deep Dive into SaaS Unit Economics

Understanding the economics of acquiring and serving each customer. **LTV calculation methods** Method 1: Simple LTV Formula: ARPA × Gross Margin ÷ Monthly Churn Rate Where: - ARPA = Average Revenue Per Account (monthly) - Gross Margin = Revenue less COGS as % - Monthly Churn Rate = % of customers lost per month Example: ARPA: £500/month Gross margin: 80% Monthly churn: 2% LTV = £500 × 80% ÷ 2% = £20,000 Implied customer lifetime: 1 ÷ 2% = 50 months (4.2 years) Lifetime gross profit: £500 × 80% × 50 = £20,000 Limitation: Assumes constant churn rate (reality: churn decreases over time) Method 2: LTV with expansion Formula: ARPA × Gross Margin ÷ (Churn Rate - Net Expansion Rate) Example: ARPA: £500/month Gross margin: 80% Monthly churn: 2% Monthly expansion rate: 1% (upsells from existing customers) LTV = £500 × 80% ÷ (2% - 1%) = £40,000 Impact: 1% expansion rate doubles LTV (from £20K to £40K) If expansion > churn (net negative churn): - LTV becomes theoretically infinite - Use DCF method instead - Example: 2% churn, 3% expansion = -1% net churn - Revenue from existing customers grows over time Method 3: Cohort-based LTV (most accurate) Track actual revenue from each customer cohort over time: | Month | Cohort revenue | Retention | Cumulative GP | |---|---|---|---| | 1 | £500 | 100% | £400 | | 3 | £475 | 95% | £1,160 | | 6 | £440 | 88% | £2,240 | | 12 | £380 | 76% | £4,080 | | 18 | £350 | 70% | £5,760 | | 24 | £330 | 66% | £7,200 | | 36 | £310 | 62% | £9,840 | Observation: Churn rate declines over time (survivors are stickier) - Month 1-6: ~2% monthly churn - Month 6-12: ~1.5% monthly churn - Month 12-24: ~1% monthly churn - Month 24+: ~0.5% monthly churn Projected LTV using cohort curve: £15,000-25,000 range This is more accurate than simple formula because it reflects actual retention patterns Method 4: DCF-based LTV Discount future cash flows at appropriate rate: | Year | Revenue | Gross profit | Discount factor (15%) | PV | |---|---|---|---|---| | 1 | £6,000 | £4,800 | 0.87 | £4,174 | | 2 | £5,400 | £4,320 | 0.76 | £3,283 | | 3 | £4,860 | £3,888 | 0.66 | £2,566 | | 4 | £4,374 | £3,499 | 0.57 | £1,995 | | 5 | £3,937 | £3,149 | 0.50 | £1,575 | DCF LTV: £13,593 Lower than simple method because: - Accounts for time value of money - More conservative (doesn't assume infinite horizon) **CAC deep dive** Fully-loaded CAC components: Sales costs: - Sales team salaries: £200K/quarter - Commissions: £50K/quarter - Sales tools (CRM, prospecting): £10K/quarter - Travel and entertainment: £5K/quarter - Sales subtotal: £265K/quarter Marketing costs: - Marketing team salaries: £80K/quarter - Paid advertising: £50K/quarter - Content creation: £15K/quarter - Events and conferences: £20K/quarter - Marketing tools: £10K/quarter - Marketing subtotal: £175K/quarter Total S&M: £440K/quarter New customers acquired: 55 Blended CAC: £440K ÷ 55 = £8,000 CAC by channel: | Channel | Spend | Customers | CAC | % of total | |---|---|---|---|---| | Organic/inbound | £80K | 25 | £3,200 | 45% | | Paid search | £60K | 10 | £6,000 | 18% | | Outbound sales | £200K | 12 | £16,667 | 22% | | Events | £40K | 5 | £8,000 | 9% | | Referrals | £10K | 3 | £3,333 | 6% | | Total | £390K* | 55 | £7,091 | 100% | *Remaining £50K is overhead/unattributed Insight: Outbound sales has 5x higher CAC than organic. If company can shift more to organic, blended CAC drops significantly. CAC by segment: | Segment | CAC | ARPA | LTV | LTV:CAC | |---|---|---|---|---| | Enterprise | £25,000 | £2,000/mo | £80,000 | 3.2:1 | | Mid-market | £8,000 | £500/mo | £20,000 | 2.5:1 | | SMB | £2,000 | £100/mo | £4,000 | 2.0:1 | | Self-serve | £200 | £30/mo | £900 | 4.5:1 | Observation: Self-serve has best LTV:CAC ratio (low-touch, low-cost acquisition). Enterprise has high absolute LTV but expensive to acquire. **Payback period analysis** Basic payback: CAC ÷ (Monthly ARPA × Gross Margin) | Segment | CAC | Monthly GM | Payback | |---|---|---|---| | Enterprise | £25,000 | £1,600 | 15.6 months | | Mid-market | £8,000 | £400 | 20.0 months | | SMB | £2,000 | £80 | 25.0 months | | Self-serve | £200 | £24 | 8.3 months | Issue: SMB payback is 25 months (above 24-month threshold) Action: Either reduce SMB CAC or increase SMB ARPA Payback with expansion: If mid-market customers expand 25% in year 1: Month 1-6 ARPA: £500 (original) Month 7-12 ARPA: £625 (after expansion) Adjusted payback: - Months 1-6 contribution: 6 × (£500 × 80%) = £2,400 - Remaining CAC: £8,000 - £2,400 = £5,600 - Month 7+ contribution: £625 × 80% = £500/month - Additional months: £5,600 ÷ £500 = 11.2 months - Total payback: 6 + 11.2 = 17.2 months (vs 20 without expansion) **LTV:CAC ratio analysis** Target ratios: | LTV:CAC | Interpretation | Action | |---|---|---| | <1:1 | Losing money per customer | Fix immediately | | 1-2:1 | Barely viable | Improve urgently | | 2-3:1 | Acceptable | Optimise | | 3-5:1 | Good | Invest in growth | | >5:1 | Excellent (or under-investing) | Accelerate spend | LTV:CAC too high (>5:1) may indicate: - Under-spending on growth - Could grow faster with more S&M investment - Missing market opportunity Example assessment: Company LTV:CAC: 6.5:1 - This seems great but may indicate under-investment - Test: Increase marketing spend 20% - If LTV:CAC stays above 3:1, continue increasing - Find the marginal LTV:CAC that's still profitable **Improving unit economics** Improve LTV: | Lever | Current | Target | LTV impact | |---|---|---|---| | Reduce churn (2% → 1.5%) | £20,000 | £26,667 | +33% | | Increase ARPA (£500 → £600) | £20,000 | £24,000 | +20% | | Improve gross margin (80% → 85%) | £20,000 | £21,250 | +6% | | Add expansion (0% → 1%) | £20,000 | £40,000 | +100% | Biggest lever: Expansion revenue (doubles LTV) Second: Reducing churn Third: Increasing ARPA Reduce CAC: | Lever | Current CAC | New CAC | Impact | |---|---|---|---| | Shift to organic (40% → 60%) | £8,000 | £6,000 | -25% | | Improve conversion (2% → 3%) | £8,000 | £5,333 | -33% | | Reduce sales cycle (90 → 60 days) | £8,000 | £6,500 | -19% | | Product-led growth | £8,000 | £4,000 | -50% | Biggest lever: Product-led growth (self-serve acquisition) **Unit economics dashboard** Monthly tracking: | Metric | Jan | Feb | Mar | Target | |---|---|---|---|---| | ARPA | £485 | £492 | £500 | £500 | | Gross margin | 78% | 79% | 80% | 80% | | Monthly churn | 2.1% | 1.9% | 2.0% | <2% | | Expansion rate | 0.8% | 0.9% | 1.0% | >1% | | LTV | £18.5K | £20.7K | £20.0K | >£20K | | Blended CAC | £8.2K | £7.8K | £8.0K | <£8K | | LTV:CAC | 2.3:1 | 2.7:1 | 2.5:1 | >3:1 | | Payback | 21mo | 20mo | 20mo | <18mo | Action items based on dashboard: 1. LTV:CAC below 3:1 target → Focus on reducing churn and increasing expansion 2. Payback above 18 months → Reduce CAC through channel optimisation 3. ARPA at target → Maintain pricing strategy