GuideCalculatorDetailed Guide

How to Build a MRR Calculator

Monthly Recurring Revenue (MRR) is the predictable revenue a subscription business earns each month. An MRR calculator helps track revenue health, forecast growth, and identify trends.

What is a MRR Calculator?

MRR is the normalized monthly value of all active subscriptions. It includes new MRR from first-time customers, expansion MRR from upgrades, and accounts for contraction MRR from downgrades and churned MRR from cancellations.

The Formula

MRR = Sum of (subscription price × quantity) for all active subscriptions
Net MRR = New MRR + Expansion MRR - Contraction MRR - Churned MRR
MRR Growth Rate = (Current MRR - Previous MRR) / Previous MRR × 100

Code Example

JavaScript

function calculateMRR(subscriptions) {
  return subscriptions
    .filter(sub => sub.status === 'active')
    .reduce((total, sub) => {
      const monthlyValue = sub.billingCycle === 'annual'
        ? sub.amount / 12
        : sub.amount;
      return total + monthlyValue;
    }, 0);
}

function calculateNetNewMRR(newMRR, expansion, contraction, churned) {
  return newMRR + expansion - contraction - churned;
}

How to Build It

1
Create subscription input form with price, quantity, and billing cycle
2
Implement MRR normalization for annual subscriptions (divide by 12)
3
Add sections for new, expansion, contraction, and churned MRR
4
Calculate and display net MRR movement
5
Show MRR growth rate and month-over-month comparisons

Key Features to Include

Automatic normalization of annual subscriptions to monthly

Breakdown by MRR type (new, expansion, contraction, churn)

Growth rate calculations with trend indicators

Cohort analysis to track MRR by customer segment

CSV import for bulk subscription data

Monetization Strategies

SaaS analytics dashboard with MRR as core feature

Freemium: basic MRR calculator free, cohort analysis paid

White-label for accounting and billing platforms

Integration marketplace for Stripe, Chargebee, etc.

Recommended Tech Stack

Frontend

React with Chart.js for MRR visualizations

Backend

Node.js API for saving calculations and integrations

Hosting

Vercel with serverless functions for API routes

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