MRR CAC and Burn Rate SaaS Metrics Calculator: Estimate Growth and Runway

How MRR, CAC and Burn Rate Work Together

I modeled a 500 customer SaaS at 79 dollars ARPU in Feb 2026 and found 42265 dollars MRR with 19 month payback and only 14.2 months runway. Growth looked fine until churn and CAC met burn. Enter customers, spend and cash in the recurring revenue tool to link momentum, efficiency and survival in one view.

SaaS lives or dies on three numbers: how much recurring revenue you add, MRR tells you momentum, CAC tells you efficiency, and burn rate tells you survival time.

Miscalculate any one, by counting annual prepay as one month of MRR, hiding sales salaries outside CAC, or confusing gross burn with net burn, and forecasts mislead investors and hiring plans.

This guide shows how to estimate all three with free online calculators, gives formulas with worked SaaS examples, compares healthy versus risky benchmarks, flags common mistakes, and answers FAQs so you can link growth to runway in one view.

1. What Are MRR, CAC and Burn Rate?

Monthly Recurring Revenue (MRR) is normalized subscription revenue per month. If you have 400 customers paying $49 per month on average (ARPU), MRR is about $19,600 and ARR is MRR times 12, or about $235,200. MRR movement splits into new logos, expansion from upsell and cross-sell, contraction from downgrades, churned from cancellations, and reactivation. Net new MRR equals new plus expansion minus contraction minus churned. Two companies with plus $3,000 net MRR differ hugely if one added $8,000 and churned $5,000 while the other added $3,500 and churned $500; the second business is far healthier.

Related is NRR, or Net Revenue Retention, which equals starting MRR plus expansion minus contraction minus churn, all divided by starting MRR. NRR above 100 percent means existing customers expand faster than they shrink. Best-in-class SMB SaaS often shows 90 to 110 percent with enterprise at 110 to 130 percent for illustration.

Customer Acquisition Cost (CAC) is fully-loaded sales plus marketing spend to win one new customer. Blended CAC equals total sales and marketing divided by new customers, while paid CAC isolates ad spend. Fully-loaded CAC must include salaries, commissions, tools, content, and events, not just ads. CAC alone is meaningless without LTV (lifetime value, approximately ARPU times gross margin times lifespan) and payback (months to recover CAC from margin). LTV to CAC at or above 3 with payback within 12 months is a common venture heuristic for SMB SaaS, longer for enterprise, used as a screening lens rather than a rule.

Burn rate and runway translate the income statement into survival time. Gross burn is total monthly cash out for payroll, rent, software, and ads. Net burn is gross burn minus revenue collected. Runway is cash in the bank divided by net burn.

Example: $900,000 cash with $85,000 expenses and $45,000 revenue gives $40,000 net burn and about 22.5 months of runway. If net burn is zero or negative, you are default-alive or profitable. Break-even revenue equals current expenses at current margin, the target that extends runway indefinitely.

Together the trio connects: MRR growth funds lower net burn, high CAC steepens burn, and churn shortens effective runway by eroding revenue. Estimate them jointly, not in silos.

2. How to Use the MRR, CAC and Burn Calculators in 3 Steps

Step 1: Enter MRR inputs to estimate momentum. In the MRR tool, type customer count, ARPU, new, expansion, and churned amounts or rates, plus gross margin percentage. The tool turns yearly plans into monthly values. Divide yearly pay by 12. Do not count $12,000 as $12,000 of MRR — it is $1,000 of MRR. Then it shows ARR, new MRR, churn, and LTV. Test What-If scenarios such as minus one point of churn versus plus 10 percent ARPU; churn reduction often wins for compounding.

Step 2: Enter costs and customers to estimate efficiency. In the CAC tool, type marketing spend plus sales spend including salaries, commissions, and tools, new customers won, ARPU, lifespan or churn, and margin. It returns blended CAC, LTV, LTV to CAC, payback months, revenue impact, and benchmark comparison. Run scenarios such as cutting ad spend 20 percent, raising ARPU 15 percent, or shortening the sales cycle, and watch payback move instantly.

Step 3: Enter cash, revenue, and expenses to estimate runway. In the burn tool, type cash balance, monthly revenue, and monthly expenses with a payroll split if helpful. It shows gross burn, net burn, runway months plus zero-cash date, break-even revenue, funding needed for an 18-month target, and a 12-month projection chart. Adjust hiring or pricing and watch runway extend or shrink. Copy results for board updates; history stays local. Keep a monthly cadence after close and freeze definitions of what counts as sales and marketing and what counts as churn, or trends will mislead.

3. Formulas + Worked SaaS Example

MRR equals the sum of normalized recurring contracts. ARR equals MRR times 12. Churn percentage equals churned MRR divided by starting MRR. CAC equals sales and marketing divided by new customers. LTV equals ARPU times margin divided by churn rate (or times lifespan). Payback equals CAC divided by ARPU times margin. Net burn equals expenses minus revenue. Runway equals cash divided by net burn. These are simplified estimates that exclude annual prepay timing, expansion nuance, and discounting.

Core formulas: MRR equals customers times ARPU. ARR equals MRR times 12. Net new MRR equals new plus expansion minus contraction minus churned. Logo churn equals lost customers divided by starting customers. Revenue churn equals churned MRR divided by starting MRR. CAC equals marketing plus sales divided by new customers. LTV equals ARPU times gross margin times lifespan months. LTV to CAC equals LTV divided by CAC. CAC payback equals CAC divided by ARPU times margin. Gross burn is monthly cash expenses. Net burn is expenses minus revenue. Runway is cash divided by net burn.

Worked example, Acme Analytics, SMB SaaS, illustrative: Start with 500 customers times $79 ARPU equals $39,500 MRR ($474,000 ARR). During the month: new plus $3,950 (50 customers times $79), expansion plus $790, contraction minus $395, churned minus $1,580 (20 customers). Net new equals 3,950 plus 790 minus 395 minus 1,580, or plus $2,765. Ending MRR is $42,265. Revenue churn is 1,580 divided by 39,500, or 4.0 percent monthly (about 38 percent annualized if compounded, which is high; target below 2 to 3 percent monthly for SMB and below 1 percent for enterprise for illustration).

CAC math: sales and marketing of $28,000 marketing plus $32,000 sales equals $60,000 with 50 new customers, so blended CAC is $1,200. At 80 percent gross margin, contribution per customer per month is $79 times 0.8, or $63.20. Payback is 1,200 divided by 63.20, or about 19 months (long versus the 12-month heuristic). Lifespan is 1 divided by 0.04, or 25 months. LTV is 79 times 0.8 times 25, or $1,580. LTV to CAC is about 1.3 times (weak and needing a pricing, churn, or CAC fix).

Burn math: $750,000 cash with $42,000 revenue and $95,000 expenses gives $53,000 net burn and about 14.2 months of runway. Break-even needs plus $53,000 revenue at current spend (about 126 percent growth) or minus $53,000 spend. Cutting $15,000 of spend plus improving churn by one point extends runway by about 5 to 6 months combined, which you can model in the burn tool What-Ifs.

4. Comparison: Healthy vs. Risky Benchmarks

Benchmarks are lenses, not laws: product-led growth with $20 ARPU differs from enterprise deals at $50,000 ACV. Still, Table 2 gives directional screening ranges commonly cited by SaaS operators and investors for illustration, varying widely by context.

Burn multiple equals net burn divided by net new ARR. Example: $53,000 monthly burn ($636,000 yearly) divided by $2,765 times 12 ($33,180 ARR added) is about 19 times, extremely inefficient against a healthy target below 2 times. This single ratio links growth spend to growth gained and is favored by investors because it punishes growth at any burn.

Use the trio together: if LTV to CAC is strong but runway is below 12 months, you have efficient growth with too little cash, so raise or slow hiring. If runway is long but NRR is below 90 percent, you have time but a leaky bucket, so fix retention before pouring CAC fuel on growth.

5. Five Mistakes That Break SaaS Math

1. Counting bookings or annual cash as MRR. A $12,000 annual prepay is $1,000 MRR, not $12,000 MRR. Counting cash spikes MRR, understates churn, and overstates LTV. Normalize every contract to monthly recurring value and separate one-time services.

2. Hiding salaries inside CAC. Claiming $150 CAC from ad spend alone while three SDRs plus tools cost $35,000 monthly is fiction. Fully-loaded CAC is often 3 to 5 times paid-only CAC. Include salaries, commissions, tools, content, and events, and segment blended versus paid versus channel views.

3. Using revenue instead of margin in LTV and payback. Seventy-nine dollars of ARPU at 60 percent margin contributes $47, not $79. Payback on revenue looks about 40 percent faster than reality. Always multiply by gross margin; low-margin SaaS with heavy hosting or support needs a higher LTV to CAC to compensate.

4. Confusing gross burn with net burn. Saying we burn $95,000 versus $53,000 net burn implies 7.9 versus 14.2 months on $750,000 cash, a very different fundraising urgency. Report both: gross shows the cost-discipline target and net decides runway. Growing revenue while holding gross flat extends runway fastest.

5. Averaging away cohort truth. Blended churn of 2 percent can hide new-cohort churn of 8 percent plus old-cohort churn of 0.5 percent. Similarly, blended CAC hides $400 product-led versus $4,000 outbound cost. Split by cohort, channel, and segment monthly, fix the worst cohort, and double down on the best. The calculators scenario modes make this fast when you save baselines and compare.

How the Math Works

MRR equals the sum of normalized recurring contracts; ARR equals MRR times 12. Churn equals churned MRR divided by starting MRR. CAC equals sales and marketing divided by new customers. LTV equals ARPU times margin divided by churn rate (or times lifespan). Payback equals CAC divided by ARPU times margin. Net burn equals expenses minus revenue; runway equals cash divided by net burn. Simplified illustrative estimates excluding prepay timing, expansion nuance, and discounting.

Keep learning: Pair with Salary Take-Home Pay Explained for hiring budgets and GST Calculator India with Examples for pricing taxes into ARPU.