Reassessment Shock Calculator

Reassessment after sale or abatement expiration can dramatically alter economics.

Prior assessed value

New assessed value

Mill rate (per $1000)

Prior annual tax

Annual tax increase

$143,000

New annual tax

$187,000

Tax shock multiple

4.3

How the math works

New tax = new assessed × mill rate. Shock = new − prior. Multiple = new ÷ prior.

$8.5M × 22/1000 = $187k new. $187k − $44k = $143k increase, 4.25x shock.

How to Use

Enter prior assessed value.
Enter new assessed value.
Enter mill rate / 1000.
Enter prior annual tax.
Read reassessment tax impact.

Frequently Asked Questions

When does reassessment happen?

At sale (California Prop 13 'change of ownership' reassessment to market, most jurisdictions similar on sale). Post-abatement expiration (cliff reassessment back to full market). Post-significant improvement (new building, major renovation above threshold). Mandatory cyclical reassessment (some states every 2-5 years). Parcel split/consolidation. Changes in use classification. Each trigger resets tax basis — buyer or post-abatement owner bears new tax.

How dramatic can the shock be?

Prop 13 California: old owner paying $30k on $300k assessed; new owner at $3M market = $300k new tax. 10x shock. Post-abatement: $50k/yr abated tax → $275k full tax = 5.5x. Florida Save Our Homes cap similar on transfer. NY non-421a buildings face 3-5x shock post-abatement. Factor shock into buyer underwriting — many institutional buyers explicitly cap offers below sellers' expectation because of shock anticipation.

Can you challenge the reassessment?

Yes. Every jurisdiction has assessment review process: board of review, superior court, special tax court. Success rate: 25-40% for residential, 40-65% for commercial (more data, more leverage). Typical reduction achieved: 5-15% off initial over-assessment. Takes 6-18 months. Tax certiorari attorneys work on contingency (20-35% of savings). Always file for review within your window — missing the window locks in for the year.

How do buyers model shock?

Forward-underwrite full market-rate property tax, not prior owner's tax. Use comp sales to estimate new assessed value. Apply jurisdiction's mill rate. For commercial, use income approach: NOI capitalized at market, then multiplied by assessment ratio. Many lenders now require buyer-tax modeling in underwriting before credit approval. Assuming prior tax is a rookie mistake that's cost buyers 50-200 bps of cap rate.