Composite metrics combine multiple pieces of data into a single score.
They're useful because they force trade-offs and provide a single direction. But they can also hide problems if used carelessly.
The Rule of 40
Formula:
Rule of 40 Score = Revenue Growth Rate % + Profit Margin %
What it means: A SaaS company with 40% growth rate and 0% profit margin scores 40. A company with 10% growth and 30% profit margins also scores 40.
Healthy benchmark:
- Startup (<$50M ARR): Score should be 30-40
- Growth stage ($50M-$500M ARR): Score should be 40-50
- Mature ($500M+ ARR): Score should be 40+
Why it works: Rule of 40 forces companies to balance growth and profitability. You can't be reckless on either dimension.
Example:
- Company A: 50% growth, -10% profit margin = Score of 40 ✓
- Company B: 20% growth, 20% profit margin = Score of 40 ✓
- Company C: 60% growth, -30% profit margin = Score of 30 ✗
Company C is being too reckless. It's growing fast but bleeding money.
Limitations:
- A company with 50% growth and -15% margin scores 35, while a company with 15% growth and 25% margin scores 40. Are they equally healthy? Not necessarily.
- It doesn't account for customer quality, churn, or efficiency improvements ahead.
- It's a rear-view mirror metric (measuring past quarters, not predicting future).
Magic Number
Formula:
Magic Number = (MRR in current month - MRR in previous month) × 12 / Sales & Marketing spend in previous month
What it means: For every $1 spent on sales and marketing, how much annual recurring revenue do you generate?
Example:
- MRR grew from $100K to $120K = $20K growth
- Sales & Marketing spend last month: $50K
- Magic Number = ($20K × 12) / $50K = 4.8
For every $1 spent on sales and marketing, you generated $4.80 in annual recurring revenue.
Healthy benchmark:
- Below 0.5: Sales and marketing spend isn't paying off
- 0.5-0.75: Healthy
- 0.75-1.0: Great
- 1.0+: Excellent (every $1 of marketing spend generates $1+ of ARR)
Why it works: It's easy to calculate and tells you if your growth investments are paying off.
Limitations:
- It's volatile month-to-month (one big deal can skew it)
- It doesn't account for the fact that sales cycles are typically 2-3 months
- It doesn't distinguish between high-quality and low-quality revenue
CAC Payback Period
Already covered in detail in "Unit Economics 101," but it's a key composite metric.
Formula:
CAC Payback Period = CAC / (Monthly Revenue × Gross Margin %)
Healthy benchmark: <12 months
Customer Lifetime Value (LTV)
Already covered in detail, but as a composite metric:
Formula:
LTV = (Monthly Profit per Customer × Average Customer Lifetime Months)
Net Revenue Retention (NRR)
For companies with expansion revenue (upsells, add-ons):
Formula:
NRR = (Revenue from existing customers last month + expansion revenue) / Revenue from existing customers month before
Example:
- Last month revenue from existing customers: $100K
- This month revenue from same customers (without new customers): $105K
- NRR = 105% (customers are spending 5% more, on average)
Healthy benchmark:
- Below 100%: Negative expansion (customers are churning or downgrading)
- 100-105%: Minimal expansion
- 105-120%: Good (customers are expanding)
- 120%+: Excellent (customers more than doubling spending over time)
Why it works: NRR tells you whether your product is becoming more valuable over time. If NRR > 100%, you can grow even if new customer acquisition stays flat.
Composite Metrics Pitfalls
❌ Pitfall 1: Using Composite Metrics to Hide Problems
Rule of 40 score of 40 might look good. But is it 50% growth + -10% margin (unsustainable) or 20% growth + 20% margin (sustainable)?
Prevention: Always look at the underlying components, not just the composite score.
❌ Pitfall 2: Ignoring Time Lag
Magic Number is calculated from last month's spend driving this month's revenue. But sales cycles are 2-3 months. The metric is lagged.
Prevention: Use leading indicators alongside composite metrics.
❌ Pitfall 3: Comparing Across Different Companies
Rule of 40 works differently for companies at different stages:
- A late-stage company with 10% growth and 40% margins scores 50 (healthy)
- An early-stage company with 10% growth and 40% margins might be dying (not growing fast enough)
Prevention: Use composite metrics to track your own business over time, not to compare with others.
How to Use Composite Metrics Effectively
- Track them monthly/quarterly: They smooth out short-term volatility
- Know the underlying components: Always understand what goes into the score
- Use them alongside leading indicators: Don't rely on them alone
- Set targets: "Our Rule of 40 score should be 45 by end of year"
- Adjust for your stage: Different companies have different targets
The Bottom Line
Composite metrics are useful when they:
- Combine multiple important factors into one direction
- Force trade-off decisions (growth vs. profitability)
- Are easy to understand and communicate
They're dangerous when they:
- Hide underlying problems
- Are used to justify ignoring other metrics
- Are compared across different companies or stages
Use them as a tool, not a crutch.