What's the difference between LTV/CAC and CAC payback — don't they measure the same thing?

They measure different problems. LTV/CAC tells you whether a customer is profitable over their lifetime. CAC payback tells you when the cash from that customer is actually back in your bank account. A SaaS with LTV/CAC of 5 but CAC payback of 24 months can still die — because for two years you're funding next month's acquisition out of past savings, not current cash flow. Bootstrappers run out of working capital long before they run out of profitable customers.

Why is 12 months the line for bootstrappable SaaS?

It's not magic — it's how monthly working capital recycles. If your CAC payback is 12 months and you're growing 10% MoM, the cash from month 1's customers is back in time to fund month 13's acquisition, with the difference funding growth on top. Below 12 months you compound naturally; between 12 and 24 months you can grow but slowly; above 24 months the math only works if someone else funds the gap (VC, debt, savings burn). David Skok's SaaStr data on 100+ companies puts the bootstrapping threshold consistently at 12-15 months.

Can I just raise prices to fix bad CAC payback?

Sometimes, with caveats. Raising ARPU 50% (say $30 → $45) cuts CAC payback by ~33%. The catch: price increases compress your top-of-funnel because your blended CAC was assuming the cheaper price point. Real-world A/B tests at indie hackers show 30-40% conversion drop on a 50% price increase — the net effect on CAC payback is usually 15-20%, not 33%. Better fix is usually churn reduction (sticky onboarding, annual prepay incentives, value-density features) which compounds without hurting acquisition.

What's a realistic monthly churn rate for indie SaaS?

It varies wildly by category. Consumer SaaS sees 5-10% monthly churn, B2B prosumer 3-5%, B2B mid-market 1-3%, enterprise <1%. Indie hackers in the consumer/prosumer band typically land at 5-7% — anyone telling you they're at 2% on $20/mo product is either measuring active churn (cancellations) instead of revenue churn (downgrades + cancellations + dormancy), or hasn't been around long enough to see year-2 cohorts.

CAC Payback > 18 Months Means You Can't Bootstrap (Even With $5K MRR)

The Two Metrics That Actually Decide

Every indie hacker has heard “LTV/CAC ≥ 3 is healthy.” Most haven’t internalized that this rule is necessary but not sufficient. We ran six unit-economic profiles through the calculator at $5K MRR, $200 CAC, and 80% gross margin to figure out where the bootstrap line actually sits.

Three numbers come out of the math:

Metric	What it measures	Bootstrappable threshold
LTV/CAC	Lifetime profitability per customer	≥ 3
CAC payback (months)	How fast cash recycles	< 12 mo
Months to day-job parity	Time until quitting math works	< 24 mo at sustainable growth

LTV/CAC alone is a vanity metric. Cash flow is what kills bootstrapped businesses, not unprofitable customers in aggregate.

Six Profiles, Same MRR — Different Outcomes

We modeled six common indie SaaS unit economics, all at $5K starting MRR with 10% MoM growth. Same revenue, different shapes:

Profile	ARPU	Churn	CAC	LTV/CAC	Payback	Verdict
Premium B2B prosumer	$50	3%	$200	6.7×	5.0 mo	Bootstrappable — comfortable margin
Standard consumer SaaS	$30	5%	$100	4.8×	4.2 mo	Bootstrappable — fast cash recycle
Sales-touch SMB	$200	3%	$1,500	3.6×	9.4 mo	Marginal — cash gets tight
Indie freemium	$10	7%	$30	3.8×	3.8 mo	Sustainable but slow growth
High-CAC consumer	$20	8%	$200	1.0×	12.5 mo	Broken — barely covers acquisition
Enterprise mini-tier	$500	2%	$5,000	4.0×	12.5 mo	Marginal — needs deep pockets

The two “marginal” profiles (sales-touch SMB and enterprise mini) both have LTV/CAC ≥ 3.6 — by the standard rule of thumb, healthy. They’re not bootstrappable because the working capital math doesn’t work. With CAC payback of 9-13 months and 10% MoM growth, you’re constantly forward-funding next month’s acquisition out of capital you haven’t recycled yet.

Where this scenario doesn’t apply

The framework above assumes a few things that aren’t always true. Counter-examples worth flagging:

Annual prepay flips the math. A $50/month plan billed annually upfront ($600 collected day one) makes CAC payback essentially zero. Most consumer SaaS doesn’t do this; most B2B can. Buffer ran on annual-prepay-funded acquisition for years.
Network-effect or viral products can grow without paid acquisition, making CAC effectively $0 — at which point the whole framework collapses to “is your churn under control?” Notion, Calendly, Linear all started here.
Product-led services with paid implementations. If 30% of revenue is one-time setup fees, payback math underestimates cash flow. Don’t include implementation revenue in MRR but do count it against effective CAC.
Seasonality compresses windows. Tax software at 80% Q1 revenue, e-commerce SaaS at 60% Q4. The “12-month payback” metric is a 12-month average — the working-capital pinch is in the off-season.
Solo founders with day jobs. If you’re running this on $0 marketing because you’re churning content on weekends, your CAC is closer to your time-cost than to dollar-cost. Different math, different decision frame.

The Honesty Correction on Day-Job Parity

The calculator’s “months to quit day job” output assumes 100% of gross profit replaces your salary. In practice that’s optimistic by 40-60%.

A worked example: Maya’s day job pays $7,000/month take-home. Her SaaS is at $5K MRR, 80% gross margin, growing 10% MoM. Calculator says she replaces day-job income at MRR = $7,000 / 0.80 = $8,750, which she hits in roughly 6 months at 10% growth.

What the calculator misses:

Self-employment tax: an extra 7.65% on top of normal income tax (the employer FICA portion she stops getting)
Health insurance: $1,200/month for a 35-year-old solo plan in a US metro, vs $200 employer-subsidized
Runway buffer: she should have 6 months of expenses ($42K) saved before quitting, otherwise the first slow month in year 2 ends the experiment
Income volatility tax: solo SaaS revenue varies ±15% MoM. The day job’s stability is worth ~10% of nominal income in optionality value

Real replacement MRR for Maya is closer to $13,000 — about 18 months at 10% growth, not 6. The calculator gives the floor; the realistic target is 1.4-1.6× that floor.

What the Churn Lever Actually Does

Of all four inputs, churn is the highest-leverage. Cutting it has compounding effects on LTV, payback, and growth. We re-ran the standard consumer profile holding everything else constant:

Monthly churn	LTV	LTV/CAC	Payback	Months to $9K MRR
8%	$300	3.0×	4.2 mo	11.0
5%	$480	4.8×	4.2 mo	8.5
3%	$800	8.0×	4.2 mo	7.2
2%	$1,200	12.0×	4.2 mo	6.7

CAC payback is unchanged because it depends on first-month gross profit, not retention. But LTV triples going from 8% to 3% churn — and the months-to-threshold drops because growth compounds against a smaller leak.

This is why “fix onboarding, then think about acquisition” is the standard bootstrap playbook. A leaky bucket grows slowly even with cheap water.

Where this calculator falls short

Steady-state assumption. We model constant CAC, constant ARPU, constant churn. Real SaaS sees CAC inflation as you saturate cheap channels (years 1-2 are SEO-cheap; year 3 you’re paying for ads), ARPU compression as you discount to retain, and churn shifts as cohort mix changes.
No expansion revenue. Healthy SaaS grows existing accounts via upsells, seat expansion, or usage-based metering. The calculator counts new customers only — net revenue retention >100% (typical for B2B) means our “months to threshold” overestimates by 20-40%.
No seasonality. Average annual numbers hide the working-capital pinch in slow months. If your SaaS is 70/30 weighted toward H1, the H2 cash flow may not survive a 24-month payback even if the annual average works.
Linear growth assumption. Compound 10% MoM forever doesn’t exist — growth flattens as TAM saturates. Use the projection for 6-12 months, not 36.

What to actually do

Run the calculator with your actual cohort numbers, not the cherry-picked good month. Pull last 90 days of cancellations from Stripe and divide by start-of-period customers — that’s your real churn.
If CAC payback > 18 months, fix one variable before quitting. Options ranked by leverage: (a) introduce annual prepay with 15% discount, (b) reduce churn via onboarding/sticky features, (c) raise prices on new customers only (grandfather existing).
Multiply the “months to day-job parity” output by 1.5 to get a realistic target. If that target is over 36 months, the day job isn’t replaceable from this product alone — either the product needs to scale faster, or you need a different relationship to the income.
Track CAC payback monthly, not LTV/CAC. LTV moves slowly and depends on churn projections that take 12+ months to validate. Payback is observable in current cash flow.
Set a working-capital floor of 6 × monthly burn before quitting anything. The calculator math is necessary but not sufficient — runway is what lets you survive the months when growth flattens.

Open the SaaS Metrics → Profitability calculator → and run your specific numbers. Pair it with the Cloud Bill Estimator to see what your infra cost does to gross margin, and the Startup Runway calculator to validate how long you can hold position while the math catches up.