Invoice Late Fee Calculator

• A CAC:LTV ratio below 1:3 usually signals unsustainable growth economics.
• Gross margin above 60% is the software benchmark; below 40% typically means a services business.
• Break-even in units tells you the sales floor you need to cover fixed costs.

1. 1Enter your revenue, cost, or customer metrics.
2. 2Set growth, margin, or retention assumptions.
3. 3Review the calculated KPI and its components.
4. 4Copy the result into your dashboard or investor update.

• Founders modelling revenue, CAC or LTV
• Marketing teams sizing campaign ROI
• Ops teams tracking unit economics
• Investors running quick diligence

• Before launching a new campaign or product
• During monthly or quarterly business reviews
• When fundraising or building a pitch model
• Before making a hiring or pricing decision

• Assumptions about growth, churn or margin
• Time period consistency (monthly vs annual)
• One-time vs recurring inputs
• Segment or cohort you're modelling

Illustrative examples using U.S. market averages. Enter your own numbers above for a personalized figure.

• Using inconsistent time periods (monthly vs annual).
• Ignoring churn or refunds when projecting revenue.

• Track cohort behaviour, not just aggregate metrics.
• Keep unit economics honest by including all variable costs.
• Sanity-check projections against the past 3–6 months of actuals.

• Fast unit-economics, NPV, IRR and payback checks for founders and operators.
• No spreadsheet gymnastics — just enter the numbers and read the result.
• Great for board decks, investor updates and internal planning.
• Formulas match CFA / MBA-standard finance textbooks.

• Assumes inputs are accurate — garbage in, garbage out.
• Does not model competitive response, macro shocks or churn cliffs.
• Point estimates only — consider a Monte-Carlo tool for probabilistic ranges.
• Should not replace a full financial model for board or investor decisions.

CAC (Customer Acquisition Cost)

Total sales and marketing spend divided by new customers acquired in the same period.

LTV (Lifetime Value)

The gross profit a customer generates across their full relationship. Healthy SaaS targets LTV:CAC of at least 3:1.

Churn

The % of customers or revenue lost in a period. Monthly churn above 5% usually signals a product-market-fit gap for SaaS.

Gross margin

Revenue minus cost of goods sold, as a % of revenue. Software is typically 70–90%; services 20–40%.

Payback period

How many months of gross profit are needed to recoup a customer's acquisition cost. Under 12 months is considered strong.

• Sanity-check the model against the last 3–6 months of actuals.
• Include all variable costs (payment fees, support, hosting) in gross margin.
• Model conservative, base, and stretch scenarios before sharing with investors.
• Track cohort-level metrics — averages hide the customers who churn fastest.

The formulas, rates and definitions used by this calculator are aligned with the following official sources:

• U.S. Small Business Administration (SBA) — Definitions for break-even, margin and small-business planning.
• Financial Accounting Standards Board (FASB) — U.S. GAAP definitions for margin, revenue and cost categories.

We use only primary sources — regulators, standards bodies and scheme operators. See our full sourcing policy for details. Sources & References Policy · Calculator Methodology · How We Verify Formulas

We continuously review and improve our calculators to keep formulas, assumptions and references accurate.

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