Online Pro Rata Wheel Calculator

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Online Pro Rata Wheel Calculator

Calculate earned and unearned premiums or contract values based on specific dates.

Total Days in Term: 0
Days Elapsed (Earned): 0
Days Remaining (Unearned): 0
Pro Rata Factor: 0.0000
Earned Amount: $0.00
Unearned (Refund) Amount: $0.00

What is a Pro Rata Wheel?

A pro rata wheel, traditionally a physical circular slide rule used by insurance agents and underwriters, is a tool designed to calculate the proportional distribution of a premium or contract value over a specific period. In modern business, an online pro rata wheel calculator automates this process by determining the exact number of days between dates to find the "earned" vs "unearned" portions of a financial commitment.

How the Pro Rata Calculation Works

The core logic of a pro rata calculation involves three primary steps:

  • Total Term Calculation: Determining the total number of days between the start and end of the original contract.
  • Elapsed Time: Identifying how many days have passed from the start date to the date of cancellation or modification.
  • Proportional Ratio: Dividing the elapsed days by the total term days to find the pro rata factor.

Typical Formula Used

The math behind the digital wheel is straightforward but requires precision with dates:

Pro Rata Factor = Days Elapsed / Total Days in Term
Earned Premium = Total Premium × Pro Rata Factor
Unearned Premium = Total Premium – Earned Premium

Example Calculation

Imagine a 12-month insurance policy costing $1,200 starting on January 1st and ending on December 31st (365 days). If the policy is canceled on April 10th:

  1. Total Days: 365
  2. Days Elapsed (Jan 1 to Apr 10): 100 days
  3. Factor: 100 / 365 = 0.27397
  4. Earned Amount: $1,200 × 0.27397 = $328.77
  5. Unearned Refund: $1,200 – $328.77 = $871.23

When to Use This Tool

This calculator is essential for insurance professionals, property managers, and subscription-based service providers. It ensures that when a contract is terminated early, the refund or final balance is calculated fairly based on actual time used, rather than arbitrary rounding.

function calculateProRata() { var startDateVal = document.getElementById('startDate').value; var endDateVal = document.getElementById('endDate').value; var cancelDateVal = document.getElementById('cancelDate').value; var totalAmount = parseFloat(document.getElementById('totalAmount').value); if (!startDateVal || !endDateVal || !cancelDateVal || isNaN(totalAmount)) { alert("Please fill in all fields with valid dates and amounts."); return; } var start = new Date(startDateVal); var end = new Date(endDateVal); var cancel = new Date(cancelDateVal); if (start >= end) { alert("End date must be after the start date."); return; } if (cancel end) { alert("Cancellation date must be within the policy period."); return; } // Convert time to days (1000ms * 60s * 60m * 24h) var msPerDay = 1000 * 60 * 60 * 24; var totalDays = Math.round((end – start) / msPerDay); var earnedDays = Math.round((cancel – start) / msPerDay); var unearnedDays = totalDays – earnedDays; var factor = earnedDays / totalDays; var earnedAmount = totalAmount * factor; var unearnedAmount = totalAmount – earnedAmount; // Display results document.getElementById('resTotalDays').innerText = totalDays; document.getElementById('resEarnedDays').innerText = earnedDays; document.getElementById('resUnearnedDays').innerText = unearnedDays; document.getElementById('resFactor').innerText = factor.toFixed(4); document.getElementById('resEarnedAmount').innerText = "$" + earnedAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resUnearnedAmount').innerText = "$" + unearnedAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('pr-results').style.display = 'block'; }

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