Calculate prorated amounts based on move-in/move-out dates
Move-In (Start Date to End of Month)
Move-Out (Start of Month to End Date)
Days in Selected Month:–
Daily Rate:–
Billable Days:–
Prorated Total:–
What is a Pro Rate Wheel Calculator?
In property management and real estate, a "Pro Rate Wheel" (often a physical cardboard wheel) is a tool used to quickly determine the prorated rent or dues for a partial month of occupancy. Whether a tenant moves in on the 15th or moves out on the 20th, calculating the exact amount owed requires precision to ensure fairness and accounting accuracy. This digital calculator replaces the manual wheel, eliminating human error and providing instant, accurate financial figures.
How the Proration Calculation Works
Proration distributes a total monthly cost across the specific number of days a service or property was used. The standard method used by this calculator—and most property management software—follows the "actual days in month" logic.
Daily Rate = Total Monthly Rate / Total Days in Month
Prorated Amount = Daily Rate × Billable Days
Note on Days in Month: The calculation varies depending on whether the month has 28, 29, 30, or 31 days. A physical wheel automatically accounts for this circular calendar logic. This digital tool does the same by detecting the specific month from your date input.
Calculation Scenarios
There are two primary scenarios for using a pro rate wheel:
Move-In Proration: The tenant gains possession of the property partway through the month. They are billed from the "Effective Date" through the last day of that month (inclusive).
Move-Out Proration: The tenant returns possession partway through the month. They are billed from the 1st of the month through the "Effective Date" (inclusive).
Example Calculation
Imagine a unit calculates a monthly rate of $1,200.00.
Scenario: Tenant moves in on September 12th.
Days in September: 30 days.
Daily Rate: $1,200 / 30 = $40.00 per day.
Billable Days: September 12 to September 30 = 19 days (inclusive).
Total Prorated Rent: $40.00 × 19 = $760.00.
Using this calculator ensures that leap years and months with varying lengths are handled correctly without the need for manual counting.
function updateLabel() {
var type = document.getElementById('calcType').value;
var label = document.getElementById('dateLabel');
if (type === 'moveIn') {
label.textContent = "Move-In Date";
} else {
label.textContent = "Move-Out Date";
}
}
function calculateProration() {
// 1. Get Input Values
var rateInput = document.getElementById('monthlyRate').value;
var dateInput = document.getElementById('effectiveDate').value;
var type = document.getElementById('calcType').value;
// 2. Validate Inputs
if (rateInput === "" || dateInput === "") {
alert("Please enter both a monthly rate and an effective date.");
return;
}
var monthlyRate = parseFloat(rateInput);
if (isNaN(monthlyRate) || monthlyRate < 0) {
alert("Please enter a valid positive number for the monthly rate.");
return;
}
// 3. Date Parsing
// We create a date object. Note: input type="date" returns YYYY-MM-DD
// We append 'T00:00:00' to ensure local time is treated correctly without timezone offset shifts causing day jumps in some browsers
var selectedDate = new Date(dateInput + 'T00:00:00');
var year = selectedDate.getFullYear();
var month = selectedDate.getMonth(); // 0-indexed (Jan is 0)
var day = selectedDate.getDate();
// 4. Calculate Total Days in the specific month
// new Date(year, month + 1, 0) gets the last day of the current month
var daysInMonth = new Date(year, month + 1, 0).getDate();
// 5. Calculate Billable Days based on Type
var billableDays = 0;
if (type === 'moveIn') {
// Logic: From selected day to end of month (Inclusive)
// Example: Sept 30 (30 days total). Move in Sept 30. 30 – 30 = 0 + 1 = 1 day.
billableDays = (daysInMonth – day) + 1;
} else {
// Logic: From 1st of month to selected day (Inclusive)
// Example: Move out Sept 5. Days = 5.
billableDays = day;
}
// 6. Calculate Financials
var dailyRate = monthlyRate / daysInMonth;
var totalProrated = dailyRate * billableDays;
// 7. Format Output
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('resDaysInMonth').textContent = daysInMonth;
document.getElementById('resDailyRate').textContent = formatter.format(dailyRate);
document.getElementById('resBillableDays').textContent = billableDays + " days";
document.getElementById('resTotal').textContent = formatter.format(totalProrated);
// 8. Show Result Box
document.getElementById('result-box').style.display = 'block';
}
// Initialize label on load
updateLabel();