Insurance Pro Rata Endorsement Calculator

Insurance Pro Rata Endorsement Calculator

Enter a positive number for an additional premium or negative for a return premium.

Calculation Summary

Days Remaining:

Pro Rata Factor:

Endorsement Premium:

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What is an Insurance Pro Rata Endorsement?

In the insurance industry, an endorsement is a change to an existing policy. When you make a change mid-term—such as adding a vehicle, increasing coverage limits, or changing your address—the insurance company calculates the "pro rata" premium. This ensures you only pay for the portion of the policy period that remains.

How the Pro Rata Calculation Works

The calculation is based on the number of days the change will be in effect until the policy expires. Unlike "Short Rate" cancellations (which include a penalty for early cancellation), pro rata is a fair-share calculation that doesn't penalize the policyholder.

The Formula:

Endorsement Amount = (Annual Premium Change) × (Days Remaining / 365)

Practical Example

Imagine you have a policy that expires on December 31st. On October 1st, you decide to add a new driver to your policy. The insurance company determines that the annual cost to add this driver is $400.

• Annual Premium Change: $400
• Days Remaining: 91 days (Oct 1 to Dec 31)
• Calculation: $400 × (91 / 365) = $99.73

You would pay an additional premium of $99.73 for the remainder of the policy term, rather than the full $400.

When to Use This Calculator

• Adding/Removing Property: When adding a new piece of jewelry or a vehicle mid-month.
• Policy Upgrades: Increasing liability limits halfway through your policy term.
• Address Changes: Moving to a higher or lower-rated ZIP code.
• Audit Adjustments: Calculating premiums for business policies after an exposure audit.

function calculateProRata() { var premiumChange = parseFloat(document.getElementById('premiumChange').value); var effectiveDateStr = document.getElementById('effectiveDate').value; var expirationDateStr = document.getElementById('expirationDate').value; if (isNaN(premiumChange) || !effectiveDateStr || !expirationDateStr) { alert("Please enter the premium change amount and both dates."); return; } var effectiveDate = new Date(effectiveDateStr); var expirationDate = new Date(expirationDateStr); if (expirationDate = 0) { document.getElementById('resultLabel').innerText = "Additional Premium:"; document.getElementById('finalAmount').style.color = "#d32f2f"; document.getElementById('finalAmount').innerText = "$" + endorsementAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); } else { document.getElementById('resultLabel').innerText = "Return Premium (Refund):"; document.getElementById('finalAmount').style.color = "#2e7d32"; document.getElementById('finalAmount').innerText = "$" + Math.abs(endorsementAmount).toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); } document.getElementById('resultArea').style.display = "block"; }