Total of all non-deductible contributions made in previous years minus previous tax-free distributions.
$
The year-end value of all your non-Roth IRAs plus any distribution/conversion amount.
$
Calculation Results
Non-Taxable Percentage:0%
Tax-Free Amount: $0.00
Taxable Amount: $0.00
Remaining Basis for Future Years: $0.00
Understanding the IRA Pro Rata Rule
The IRS Pro Rata rule determines the taxation of withdrawals or Roth conversions from Traditional IRAs when the account owner holds both "basis" (after-tax/non-deductible contributions) and "pre-tax" (deductible contributions and earnings) funds. The IRS does not allow you to simply choose to convert only the after-tax portion; instead, it views all your non-Roth IRAs as one single pool.
The Formula Used
The calculation follows this specific logic used on IRS Form 8606:
Step 1: Total Basis ÷ Total IRA Balance = Tax-Free Percentage
If you have a large balance in a rollover IRA from a previous 401(k), attempting a "Backdoor Roth IRA" contribution (making a non-deductible contribution and then immediately converting it) will trigger the pro rata rule. You will owe taxes on a portion of that conversion proportional to the amount of pre-tax money across all your IRAs.
Realistic Example
Suppose you have $94,000 in a Rollover IRA (pre-tax) and you contribute $6,000 to a Traditional IRA as a non-deductible contribution (basis). Your total IRA value is $100,000. Your "basis" is 6% of the total. If you convert that $6,000 to a Roth IRA, only $360 (6% of $6,000) is tax-free. The remaining $5,640 is subject to income tax.
function calculateProRata() {
var basis = parseFloat(document.getElementById("nonDeductibleBasis").value);
var totalValue = parseFloat(document.getElementById("totalIraValue").value);
var conversion = parseFloat(document.getElementById("conversionAmount").value);
var resultsDiv = document.getElementById("resultsArea");
// Basic validation
if (isNaN(basis) || isNaN(totalValue) || isNaN(conversion) || totalValue totalValue) {
alert("Basis cannot be greater than the total IRA value.");
return;
}
// Pro Rata Logic
// Ratio of non-taxable funds to total funds
var ratio = basis / totalValue;
// Calculate the portions of the current transaction
var taxFreeAmount = conversion * ratio;
var taxableAmount = conversion – taxFreeAmount;
// Remaining basis for next year
var remainingBasis = basis – taxFreeAmount;
// Formatting results
document.getElementById("taxFreePercent").innerText = (ratio * 100).toFixed(2);
document.getElementById("taxFreeAmount").innerText = taxFreeAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("taxableAmount").innerText = taxableAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("remainingBasis").innerText = remainingBasis.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Display results
resultsDiv.style.display = "block";
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}