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Form 4684
Form 4684

Form 4684Casualties and Thefts

2 — Cost or Adjusted Basis Updated for tax year 2025

Does this apply to you?

  • You are calculating a casualty or theft loss on personal-use property
  • You purchased the property and know the original cost
  • You inherited or received the property as a gift and need to determine its basis
  • You made improvements to the property that increased its basis

Easy to overlook

Inherited property uses fair market value at date of death, not original cost If you inherited a home from a parent, your basis is the fair market value on the date of death (the stepped-up basis), not what the parent originally paid. Using the parent’s purchase price from decades ago dramatically understates your basis and inflates your deductible loss. 1 IRS Publication 551 — Basis of Assets

Permanent improvements increase your basis A new roof, remodeled kitchen, or added bathroom increases the cost basis of your home. If you paid $250,000 for the house and later spent $40,000 on a roof and renovation, your adjusted basis is $290,000. Forgetting to include improvements understates your basis, which reduces the loss you can claim. 2 IRS Publication 547 — Casualties, Disasters, and Thefts

Watch out for this

Using the current market value instead of your cost basis. Line 2 asks for what you paid (adjusted for improvements and prior losses), not what the property is worth today. Market appreciation is irrelevant. If you bought a house for $200,000 and it is now worth $400,000, line 2 is $200,000 (plus any improvements). The current value affects line 5 and line 6 (fair market value before and after the casualty), not line 2.

Footnotes

  1. IRS Publication 551, Basis of Assets, Inherited Property. https://www.irs.gov/pub/irs-pdf/p551.pdf

  2. IRS Publication 547, Casualties, Disasters, and Thefts, Figuring a Loss. https://www.irs.gov/pub/irs-pdf/p547.pdf

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