How to Write a Supplement Letter That Gets Approved

What Is a Supplement Letter?

A supplement letter is a formal written request to an insurance carrier asking for additional payment on a claim. It itemizes the line items missing from the original estimate, provides the code or industry justification for each item, and requests specific dollar amounts.

A strong supplement letter reads like documentation — not a complaint.

The Anatomy of a Winning Supplement Letter

1. Header Information

Your letter should open with:

Claim number

Policy number

Insured name and property address

Date of loss

Your company name and license number

Date of the letter

2. Introduction

One paragraph stating that you have reviewed the carrier's estimate dated [DATE] and identified the following line items that were not included in the scope.

Do not accuse the adjuster of bad faith. Keep it factual.

3. The Line Item Table

The core of the supplement letter is a table that lists each missing item with:

| Line Item | Xactimate Code | Quantity | Unit Price | Total | Justification | |-----------|---------------|----------|-----------|-------|---------------| | Drip Edge | RFG DRPEDGE | 180 LF | $1.25/LF | $225 | IRC R905.2.8.5 | | Starter Strip | RFG SSTARTER | 12 SQ | $18.00/SQ | $216 | GAF Installation Manual |

Each row needs:

The specific Xactimate line item code

Quantity and unit

Dollar amount

Code section, manufacturer requirement, or industry standard that requires it

4. Supporting Documentation

Reference any attached documents:

Applicable IRC code sections (printed)

Manufacturer installation guides

Photos of the specific area

Local building code amendments

5. Summary and Request

Close with a total dollar amount requested and a specific request for the carrier to update the estimate or issue a supplemental payment.

6. Professional Closing

Sign with your name, title, company, license number, and contact information.

Common Mistakes That Get Supplements Denied

Vague language — "This item should be included" without citing why

No code references — Claims without citations are easy to deny

Wrong Xactimate codes — Using incorrect codes undermines your credibility

Missing photos — Photos supporting each item dramatically increase approval rates

Hostile tone — Adversarial language triggers defensive responses

How EstimateDelta Writes the Letter For You

[EstimateDelta](/pricing) generates a professionally formatted supplement letter with:

Correct Xactimate codes for every line item

Specific IRC citations and state code amendments

Dollar amounts based on Xactimate pricing

A complete supplement pack ready to submit

[Generate your supplement letter →](/pricing)