SaaS Financial Modeling & Metrics
A SaaS business is a math machine. If you don't know your numbers, you're guessing. This skill makes unit economics legible — MRR, CAC, LTV, churn, burn rate — clear enough to make decisions, rigorous enough to be trusted.
Core Principles
- A SaaS business is a math machine. If you don't know your numbers, you're guessing.
- Unit economics tell the truth about your business long before your bank account does.
- The only financial model that matters for a solo founder is one that fits on a single spreadsheet and gets updated monthly.
- Revenue is vanity. Margin is sanity. Cash flow is reality.
- Every metric should answer a specific question: "Should I spend more here?" or "Is this working?"
The Quit Number
Before building anything, calculate what it takes to replace your income:
Monthly personal burn (after taxes):
Rent/mortgage: $______
Insurance: $______
Food/living: $______
Debt payments: $______
Everything else: $______
Safety buffer (20%): $______
= Monthly nut: $______
Required MRR to quit:
Monthly nut ÷ 0.70 = $______
(0.70 accounts for taxes, SaaS costs, and variance)
At your target price point ($X/mo):
Required MRR ÷ Price = customers needed
Timeline:
Customers needed ÷ realistic monthly growth rate = months to quitReality check: If you need 500+ customers at $29/mo to quit, that's an 18-36 month journey. Plan accordingly.
Personal Constraint Budget
Runway calculation:
Current savings available for this venture: $______
Monthly burn while building (no revenue): $______
Savings ÷ Monthly burn = months of runway: ______
Hard deadline: Date you MUST have revenue or go back to employment.
Startup costs (one-time):
Domain + hosting (year 1): $100-500
LLC formation: $50-500
Tools (analytics, email): $0-200/mo
Paid acquisition test: $500-1,000
Legal (if needed): $500-2,000
= Total launch cost: $______
Monthly operating costs (once live):
Hosting/infra: $______
SaaS tools: $______
Email service: $______
Payment fees: $______
= Monthly opex: $______Core SaaS Metrics
The Metrics That Matter (and only these)
Monthly Recurring Revenue (MRR)
MRR = Sum of all active monthly subscription amounts
MRR breakdown:
New MRR: Revenue from new customers this month
Expansion MRR: Revenue from upgrades/seat additions
Contraction MRR: Revenue lost from downgrades
Churned MRR: Revenue lost from cancellations
Net New MRR: New + Expansion - Contraction - ChurnedAnnual Recurring Revenue (ARR)
ARR = MRR × 12
(Only use this once MRR is relatively stable. Don't annualize your first month.)Customer Acquisition Cost (CAC)
CAC = Total acquisition spend ÷ New customers acquired (in same period)
Include: Ad spend, outreach tools, content costs, your time (value it at $0
for solo founder or at your opportunity cost — be consistent).
By channel:
SEO CAC: Content costs ÷ SEO-attributed signups
Paid CAC: Ad spend ÷ Paid-attributed signups
Outreach CAC: Tool costs ÷ Outreach-attributed signupsLifetime Value (LTV)
Simple LTV:
LTV = ARPU ÷ Monthly churn rate
Example:
ARPU = $49/mo, Monthly churn = 5%
LTV = $49 ÷ 0.05 = $980
With gross margin:
LTV = (ARPU × Gross margin %) ÷ Monthly churn rateLTV:CAC Ratio
LTV:CAC = LTV ÷ CAC
Benchmarks:
< 1:1 You lose money on every customer. Stop spending.
1-3:1 Unsustainable. Improve retention or reduce CAC.
3:1 Healthy target for most SaaS.
> 5:1 You're probably underinvesting in growth.CAC Payback Period
Payback = CAC ÷ (ARPU × Gross margin %)
Example:
CAC = $150, ARPU = $49/mo, Gross margin = 85%
Payback = $150 ÷ ($49 × 0.85) = 3.6 months
Benchmarks:
< 6 months: Excellent for solo founder
6-12 months: Acceptable
> 12 months: Dangerous without fundingChurn Rate
Logo churn (customer count):
Customers lost this month ÷ Customers at start of month
Revenue churn (MRR):
MRR lost this month ÷ MRR at start of month
Net revenue retention (NRR):
(MRR at start + Expansion - Contraction - Churn) ÷ MRR at start
NRR > 100% means existing customers grow faster than they churn.
Benchmarks:
Logo churn < 5%/mo: Acceptable early stage
Logo churn < 3%/mo: Good
Revenue churn < 2%/mo: Target
NRR > 100%: Excellent (expansion revenue working)Unit Economics Calculation
Build this table monthly:
| Metric | Month 1 | Month 2 | Month 3 | ... |
|---------------------------|---------|---------|---------|-----|
| New customers | | | | |
| Churned customers | | | | |
| Total customers (end) | | | | |
| MRR | | | | |
| Net new MRR | | | | |
| Revenue (collected) | | | | |
| COGS (hosting, APIs, etc) | | | | |
| Gross profit | | | | |
| Gross margin % | | | | |
| Total acquisition spend | | | | |
| CAC | | | | |
| LTV | | | | |
| LTV:CAC | | | | |
| Payback (months) | | | | |
| Operating expenses | | | | |
| Net profit/loss | | | | |
| Cash balance | | | | |
| Runway (months) | | | | |Revenue Mix Model
Map your revenue sources:
Primary revenue:
Monthly subscriptions: $X/mo × estimated customers = $______
Annual subscriptions: $Y/yr × estimated customers = $______
Secondary revenue (if applicable):
Usage-based overage: Estimated average overage/customer = $______
One-time setup fees: $Z × new customers/month = $______
Consulting/services: Hours/month × rate = $______
Revenue mix target:
Recurring %: ____% (target >80%)
One-time %: ____% (keep <20%)
Services %: ____% (keep <10% — doesn't scale)Essential Metrics Dashboard
Track weekly, review monthly:
Growth metrics:
- MRR (absolute and growth rate)
- New signups this week
- Activation rate (signups → activated)
- Conversion rate (activated → paying)
Retention metrics:
- Monthly logo churn rate
- Monthly revenue churn rate
- Net revenue retention
Economics metrics:
- CAC by channel
- LTV:CAC ratio
- Gross margin %
- Cash runway (months)
Leading indicators (predict future revenue):
- Traffic to marketing site
- Trial starts
- Feature adoption rates
- Support ticket volume (rising = problems ahead)
Financial Forecasting (Simple)
Don't build a complex model. Use this:
Conservative monthly growth rates by stage:
Pre-revenue to $1K MRR: add 5-15 customers/month
$1K-$5K MRR: 10-20% MRR growth/month
$5K-$20K MRR: 5-15% MRR growth/month
$20K+ MRR: 3-8% MRR growth/month
3-month forecast:
Current MRR × (1 + monthly growth rate)^3 = projected MRR
Break-even forecast:
Monthly opex ÷ ARPU = customers needed to break even
Customers needed ÷ monthly new customers = months to break evenWhen the Numbers Say Stop
Red flags that mean pivot or stop:
- LTV:CAC < 1 after 3+ months of trying to improve it
- Monthly churn > 10% with no clear fix
- CAC increasing month over month despite optimizations
- Activation rate < 20% (product-market fit problem)
- Revenue plateaus for 3+ months despite active effort
- Cash runway < 3 months with no path to profitability
Related Skills
- accounting — Bookkeeping, tax prep, and financial operations
- pricing — Set prices that support healthy unit economics
- analytics — Track the product metrics that feed financial models
- ads — CAC tracking and paid acquisition budgeting