365 Days (Standard Year)
360 Days (Commercial/Banking)
366 Days (Leap Year)
$
Enter amount to calculate actual daily cost.
Daily Percentage Rate (DPR):0.0000%
Daily Interest Cost:$0.00
Est. Monthly Interest (30 Days):$0.00
Effective Annual Rate (EAR):0.00%
Understanding the Daily Percentage Rate (DPR)
The Daily Percentage Rate (DPR) is a crucial metric often overlooked by borrowers and investors alike. While financial institutions typically advertise the Annual Percentage Rate (APR), interest on credit cards and many loans is actually calculated and accrued on a daily basis. This calculator helps you convert that annual figure into the precise daily rate applied to your balance.
The Core Formula:
DPR = APR รท 365 (or 360)
For example, a credit card with an 18% APR using a 365-day year has a daily rate of approximately 0.0493%.
Why DPR Matters for Credit Cards
Credit card issuers use your DPR to calculate finance charges at the end of each billing cycle. They take your average daily balance and multiply it by the DPR, then multiply that by the number of days in the billing cycle. Even a small difference in the daily rate can compound significantly over time if balances are carried forward.
360 vs. 365 Day Basis
Different financial products use different day count conventions:
365 Days: The most common standard for consumer credit cards and personal loans.
360 Days: Often used in commercial lending, corporate bonds, and some mortgage calculations. This is known as the "banker's year."
366 Days: Utilized during leap years by some institutions to ensure precise interest calculations.
Daily Compounding vs. Simple Interest
It is important to note the difference between nominal rates and effective rates. While the DPR is a simple division of the APR, the Effective Annual Rate (EAR) takes compounding into account. If your interest compounds daily (as it often does with credit cards), the actual amount you pay per year is slightly higher than the stated APR. Our calculator provides the EAR to give you a complete picture of the cost of borrowing.
function calculateDailyRate() {
// 1. Get input values
var aprStr = document.getElementById('aprInput').value;
var daysBasisStr = document.getElementById('daysBasis').value;
var balanceStr = document.getElementById('balanceInput').value;
// 2. Parse values
var apr = parseFloat(aprStr);
var daysBasis = parseInt(daysBasisStr);
var balance = parseFloat(balanceStr);
// 3. Validation
if (isNaN(apr) || apr < 0) {
alert("Please enter a valid positive Annual Percentage Rate (APR).");
return;
}
// Default balance to 0 if empty or invalid, just to show rate
if (isNaN(balance) || balance < 0) {
balance = 0;
}
// 4. Calculate DPR (Daily Percentage Rate)
// Formula: APR / Days
var dpr = apr / daysBasis;
// 5. Calculate Monetary Costs
// Daily Cost = Balance * (DPR / 100)
var dailyCost = balance * (dpr / 100);
// Monthly Cost (Simple projection for 30 days)
var monthlyCost = dailyCost * 30;
// 6. Calculate Effective Annual Rate (EAR)
// Formula: ((1 + (APR/100)/Days)^Days – 1) * 100
// This shows the effect of daily compounding
var rateDecimal = apr / 100;
var ear = (Math.pow((1 + (rateDecimal / daysBasis)), daysBasis) – 1) * 100;
// 7. Update the DOM
document.getElementById('resultContainer').style.display = 'block';
// Formatting:
// DPR usually needs 4-5 decimal places to be useful (e.g., 0.0493%)
document.getElementById('dprOutput').innerText = dpr.toFixed(5) + "%";
// Currency formatting
document.getElementById('dailyCostOutput').innerText = "$" + dailyCost.toFixed(2);
document.getElementById('monthlyCostOutput').innerText = "$" + monthlyCost.toFixed(2);
// EAR formatting
document.getElementById('earOutput').innerText = ear.toFixed(3) + "%";
}