Pro rata is a Latin term meaning "in proportion." In financial and legal contexts, a pro rata calculation determines the proportional share of a total amount based on the time used. While physical "pro rata wheels" were once common tools for insurance agents and landlords, this digital calculator provides the same precision instantly.
How to Use the Pro Rata Wheel Calculator
To find the proportional amount, follow these three steps:
Total Amount: Enter the full cost for the entire period (e.g., monthly rent or an annual subscription fee).
Billing Cycle: Select how many days are in the full period. For a standard month, this is usually 30 or 31.
Days to Bill: Enter the specific number of days the service was actually used or the number of days remaining.
Practical Example:
If your monthly rent is 2,000 and the month has 31 days, but you move in on the 20th, you are staying for 12 days.
Calculation: (2,000 / 31) × 12 = 774.19.
Why Accuracy Matters
Using a pro rata wheel or calculator ensures that neither party is overcharged. It is commonly used for:
Real Estate: Moving in or out mid-month.
Subscriptions: Upgrading or canceling services halfway through a billing cycle.
Insurance: Calculating returned premiums when a policy is cancelled early.
Payroll: Adjusting salary for employees starting or leaving mid-pay period.
function calculateProRata() {
var fullAmount = document.getElementById('fullAmount').value;
var cycleDays = document.getElementById('cycleDays').value;
var usedDays = document.getElementById('usedDays').value;
var resultDiv = document.getElementById('proRataResult');
// Validation
if (fullAmount === "" || usedDays === "" || fullAmount <= 0 || usedDays cycleNum) {
resultDiv.style.display = "block";
resultDiv.className = "result-error";
resultDiv.innerHTML = "Days to bill cannot exceed the total days in the cycle.";
return;
}
// Pro Rata Logic: (Total / Days in Period) * Days Used
var dailyRate = amountNum / cycleNum;
var proRataShare = dailyRate * usedNum;
var formattedShare = proRataShare.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
var dailyRateFormatted = dailyRate.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
resultDiv.style.display = "block";
resultDiv.className = "result-success";
resultDiv.innerHTML = "Pro Rata Share: " + formattedShare + "" +
"Daily Rate: " + dailyRateFormatted + " per day";
}