The core distinction
| Comparison aspect | First-party claim | Third-party claim |
|---|---|---|
| Who you claim against | Your own insurer | Another driver's insurer |
| Basis of the claim | Your own policy's contract terms | Their legal liability for the accident |
| Fault typically matters? | Often less (depends on coverage type) | Central — liability usually must be established |
| Deductible? | Yours may apply (collision/comprehensive) | Generally none — you're not the policyholder |
Why the NAIC model act matters here
The National Association of Insurance Commissioners' Unfair Claims Settlement Practices Act is a model law — a template most states have adopted in some form — that defines a "first party claimant" as someone asserting a right to payment under their own policy, and sets baseline standards insurers must meet for prompt, reasonable claims handling for both first- and third-party claimants. Because it's a model act, the specific rules that actually apply to you depend on how your state enacted (and possibly modified) it.
What varies by state: exactly which claims-handling standards apply, how strictly they're enforced, and whether they create a private right to sue for violations, all differ by state. Check your own state insurance department's consumer resources for your state's specific rules.
Why the distinction affects your total-loss or DV claim
A first-party total-loss claim runs through your own policy's ACV/deductible/loan-payoff mechanics — exactly what the Settlement Check Breakdown calculator traces. A third-party diminished-value claim instead depends on the other driver's liability and your state's rules on whether first-party or third-party DV claims are even recognized — which varies significantly and should be confirmed with your state insurance department or an attorney.
What this guide cannot tell you
It cannot tell you which type of claim applies to your specific accident, or what your state's specific claims-handling timeline requirements are. For the diminished-value question specifically, see Does Your State Allow a First-Party Diminished Value Claim?