How to Calculate Partial Reassessment Under Prop 19: A Step-by-Step Guide

When an inherited California home is worth more than the Proposition 19 value limit, the property is partially reassessed rather than fully reassessed. You keep part of the low tax base and pay market rates on the rest. This page shows you how to calculate the exact number, using figures you can pull from your own property tax bill.

The full formula is:

New taxable value = factored base year value + (market value minus value limit) where value limit = factored base year value + $1,044,586

And here is the shortcut most guides miss. Because the base year value appears on both sides, it cancels out. Whenever the home exceeds the limit:

New taxable value = market value minus $1,044,586

Both routes give the same answer. Run the long version to understand what is happening, then use the short version to check yourself.

Before You Calculate: Confirm the Exclusion Applies

The math only matters if the property qualifies. Confirm three things first.

The home was the parent’s or grandparent’s principal residence. A rental or second home receives no exclusion at all and is reassessed to full market value with no cap. There is no partial reassessment to calculate.

The heir moves in within one year and claims the homeowners’ exemption. Miss this and the home is fully reassessed regardless of value.

The transfer happened on or after February 16, 2021. Earlier transfers fall under Proposition 58, which had no value cap on the family home.

If any of those fail, stop. The answer is full market value.

Step 1: Find Your Factored Base Year Value

This is the number the county has been taxing, not what the parent paid.

Your factored base year value is the original purchase price plus the annual inflation adjustments Proposition 13 allows, capped at two percent a year, plus the assessed value of any additions or major improvements.

Where to find it: the annual property tax bill, the assessor’s annual value notice, or the county assessor’s online parcel lookup. Look for a line labeled assessed value, net taxable value, or factored base year value. Do not use the parent’s original purchase price, because decades of adjustments sit between the two.

For this walkthrough, use a factored base year value of $400,000.

Step 2: Establish Market Value at the Date of Transfer

This is fair market value on the date of death, not today’s value and not what the family later sells it for.

The county assessor makes this determination, and it is the number that governs. If the estate obtained a date-of-death appraisal, that appraisal usually informs it. Before the assessor’s notice arrives, a professional appraisal or a broker’s opinion of value gives you a working estimate.

For this walkthrough, use a market value of $1,900,000.

Step 3: Calculate the Value Limit

Add the current exclusion amount to your factored base year value.

$400,000 + $1,044,586 = $1,444,586

That figure is the ceiling. Everything below it passes at the low base.

Step 4: Compare Market Value to the Limit

Two outcomes, and only one requires further math.

Market value at or below the limit. No reassessment. The base year value carries over unchanged, and the heir pays roughly what the parent paid. A home worth $1,300,000 against this $1,444,586 limit falls entirely inside it.

Market value above the limit. Partial reassessment. Continue to step five.

Here $1,900,000 exceeds $1,444,586, so the calculation continues.

Step 5: Calculate the Excess

Subtract the limit from market value.

$1,900,000 minus $1,444,586 = $455,414

This is the only portion that gets reassessed.

Step 6: Add the Excess to the Base

$400,000 + $455,414 = $855,414

That is the new taxable value.

Check it with the shortcut. $1,900,000 minus $1,044,586 = $855,414. The two methods agree, as they always will.

Step 7: Convert to an Annual Tax Bill

Multiply the new taxable value by your tax rate. The basic California rate is one percent, and most counties add voter-approved bonds and special assessments that bring the effective rate to roughly 1.1 to 1.25 percent. Your current tax bill shows the actual rate for the parcel.

At one percent:

• The parent was paying on a taxable value of $400,000, roughly $4,000 a year.
• With partial reassessment, a taxable value of $855,414, roughly $8,554 a year.
• With full reassessment and no exclusion, a taxable value of $1,900,000, roughly $19,000 a year.

The exclusion is worth roughly $10,450 a year here. Substantial, but well short of the complete protection the old rules provided.

Three Worked Examples

The same base of $400,000, so the limit stays $1,444,586 throughout.

Example A, market value $1,100,000. Below the limit. New taxable value $400,000, annual tax roughly $4,000. Nothing changes.

Example B, market value $1,600,000. Above the limit by $155,414. New taxable value $400,000 + $155,414 = $555,414, annual tax roughly $5,554. Shortcut check: $1,600,000 minus $1,044,586 = $555,414.

Example C, market value $2,500,000. Above the limit by $1,055,414. New taxable value $1,455,414, annual tax roughly $14,554. Shortcut check: $2,500,000 minus $1,044,586 = $1,455,414. Compare to $25,000 with no exclusion at all.

Notice the pattern: as market value climbs, the exclusion saves a fixed amount of taxable value, so the dollar benefit stays roughly constant while the percentage benefit shrinks.

Common Mistakes

Using the purchase price instead of the factored base year value. The parent’s 1978 purchase price is far below the value the county actually taxes today. Using it understates the base and produces a wrong answer in both directions.

Using today’s market value instead of the date-of-death value. The valuation date is fixed at the transfer. A market that moved afterward does not change it.

Applying $1,044,586 as a straight cap on the home’s value. It is not a ceiling on the home. It is an amount added to your base to produce the ceiling, and it is why two families with identical homes but different bases face different limits.

Assuming the figure is permanent. It changes every other year. Transfers before February 16, 2025 used $1,022,600, and a new amount takes effect February 16, 2027.

Forgetting that the whole calculation is conditional. None of it applies unless the heir moves in within a year and files the homeowners’ exemption.

What to Do With Your Answer

The number tells you what the property costs to hold, which is the input to every decision that follows.

If the increase is modest, keeping the home is usually straightforward, and the calculation mainly confirms the filings are worth making.

If the increase is steep, the family faces a real question about whether the heir can carry the annual cost. Answering it before the one-year deadline is far better than discovering the number afterward.

Either way, verify against the assessor’s determination. Your calculation is an estimate until the county issues its value notice. If the county’s number differs materially from a supportable appraisal, there is an appeal process, and the deadline for it is short.

Summary

• Partial reassessment applies when a qualifying inherited home exceeds the Proposition 19 value limit.
• The value limit is the factored base year value plus $1,044,586, in effect through February 15, 2027.
• If market value is at or below the limit, the base carries over unchanged.
• If it is above, only the excess is added to the base.
• The shortcut for any home above the limit is market value minus $1,044,586.
• Use the factored base year value from the tax bill, not the original purchase price, and the date-of-death market value, not today’s.
• The calculation applies only if the heir moves in within one year and files the homeowners’ exemption.

Get the Full Picture

Read the book. Prop 19 Hero works through the value limit calculation alongside the filing steps and the traps that void the exclusion before the math ever matters. Find it on Amazon.

Talk to Bart. If you want the numbers run against your family’s actual base year value and a realistic date-of-death valuation, Bart Hubbard can do that with you. Reach out at Prop19Hero.com.