SaaS Growth Metrics Calculator
Lightbridge.ai's SaaS Growth Metrics Calculator computes five core SaaS efficiency and retention metrics, the Rule of 40, net revenue retention, gross revenue retention, the LTV:CAC ratio, and CAC payback period, from a company's own recurring-revenue and cost inputs. Every formula matches the definitions already published on Lightbridge.ai's SaaS metrics guides.
Recurring revenue for the period
Monthly recurring revenue at the start of the period. Required.
Recurring revenue added by newly acquired customers during the period.
Upsell, cross-sell, and seat growth from existing customers.
Downgrades and seat reductions from customers who stayed.
Recurring revenue lost to full cancellations.
Customers and acquisition spend
Used to calculate ARPA (average revenue per account).
Used as the CAC denominator.
Fully loaded S&M spend for the same period. Used as the CAC numerator.
Margins
Revenue minus cost of goods sold, divided by revenue. Feeds LTV and CAC payback.
This calculator uses EBITDA margin as the Rule of 40 profitability term, the same default used on the SaaS Unit Economics guide.
Enter at least a starting MRR to see your results.
The five metrics this calculator computes, and the formula behind each.
Every result on screen traces back to a formula already published on Lightbridge.ai's SaaS metrics guides. Nothing here is a new or simplified variant.
Rule of 40
Growth rate percent plus profitability margin percent. This calculator uses EBITDA margin as the profitability term, the same default stated on the SaaS Unit Economics guide.
Net Revenue Retention (NRR)
(Starting MRR plus expansion minus contraction minus churn) divided by starting MRR. Can exceed 100% because expansion is included.
Gross Revenue Retention (GRR)
(Starting MRR minus contraction minus churn) divided by starting MRR. Excludes expansion, so it is capped at 100% and floored at 0%.
LTV:CAC ratio
Customer lifetime value, (ARPA times gross margin percent) divided by revenue churn rate, divided by customer acquisition cost, sales-and-marketing spend divided by new customers.
CAC payback period
CAC divided by (ARPA times gross margin percent), expressed in months. Answers how long it takes gross-margin-adjusted revenue to repay acquisition cost.
Ending MRR and ARR run-rate
Starting MRR plus new, expansion, minus contraction, minus churned MRR, then ARR equals that ending MRR times twelve. Shown for context alongside the five metrics above.
For the full definitions, worked examples, and directional benchmark ranges behind these formulas, read SaaS unit economics, net revenue retention vs gross revenue retention, annual recurring revenue, and the SaaS metrics glossary.
A calculator gives you the number. Lightbridge.ai reads what it means.
A single Rule of 40 score or LTV:CAC ratio rarely tells the whole story on its own. Lightbridge.ai reads these figures together, against the assumptions behind them, and against the recurring-revenue system that produced them, which is how a clean calculator result turns into a defensible operating plan.
The recurring-revenue mechanics behind every number here, billing, recognition, and the system of record, sit with Lightbridge ERP. For the wider operating model and the path to scale, see technology strategy advisory.
SaaS Growth Metrics Calculator: frequently asked questions
- What does the SaaS Growth Metrics Calculator compute?
- The calculator takes your starting MRR, new, expansion, contraction, and churned MRR, customer counts, sales-and-marketing spend, gross margin, and EBITDA margin, and computes five metrics instantly: the Rule of 40 score, net revenue retention (NRR), gross revenue retention (GRR), the LTV:CAC ratio, and CAC payback period in months. It also shows your ending MRR and the equivalent ARR run-rate (MRR x 12).
- How does this tool calculate the Rule of 40?
- It adds your period revenue growth rate, computed from the ending MRR against the starting MRR you entered, to the EBITDA margin percentage you enter. That matches the formula on the SaaS Unit Economics guide: growth rate percent plus profitability margin percent, with EBITDA margin as Lightbridge.ai's default profitability term. A combined score of 40 or more is the benchmark widely cited by SaaS investors, though the profitability term is variable across companies and this tool always states which one it uses.
- How is NRR calculated, and why can it exceed 100%?
- NRR equals (starting MRR plus expansion minus contraction minus churn) divided by starting MRR, expressed as a percentage. Because expansion revenue from existing customers sits in the numerator, a cohort that expands faster than it loses to contraction and churn can push NRR above 100%. This is the identical formula used on the Net Revenue Retention vs Gross Revenue Retention guide, including its worked 105% NRR example.
- What is a good LTV:CAC ratio?
- A 3:1 ratio of customer lifetime value to customer acquisition cost is the widely cited heuristic for healthy SaaS unit economics, not a GAAP standard or a guaranteed target. The ratio the calculator shows is only as reliable as the churn rate and gross margin you enter, since LTV is calculated as (ARPA times gross margin percent) divided by revenue churn rate. Read the ratio alongside those underlying inputs rather than as a standalone score.
- How is CAC payback period calculated?
- CAC payback period in months equals CAC divided by (ARPA times gross margin percent), the same formula defined in the SaaS Metrics Glossary. It answers how many months of gross-margin-adjusted revenue it takes to recover the cost of acquiring a customer. Many SaaS teams watch for a payback period under twelve to eighteen months, though the right target depends on segment, contract length, and funding position.
- What happens to the numbers I enter into the calculator?
- Every metric is calculated in your browser the moment you click Calculate, with no submission required to see your results. If you choose to have a copy emailed to you, your inputs and computed scores are included in that submission so a Lightbridge.ai advisor can follow up with real context. There is no account and no saved history beyond that single notification.
- Are the metrics on this calculator GAAP measures?
- No. The Rule of 40, NRR, GRR, LTV:CAC, and CAC payback are SaaS-finance conventions with variable definitions across companies and investors, not requirements under GAAP, FASB, or any accounting standard. This calculator states the exact formula behind every result, and the SaaS Metrics Glossary defines each term in full. Statutory revenue recognition is a separate discipline governed by ASC 606, which Lightbridge ERP covers. This tool is general information, not financial, accounting, or investment advice.
From a calculated score to a growth-finance plan.
When the question shifts from what your Rule of 40 or LTV:CAC number is to what it says about your business, Lightbridge.ai reads these SaaS growth metrics against the assumptions behind them and turns the numbers into an operating plan.