Los Alamos property tax runs 23.737 mills on residential property and 29.207 mills on non-residential property for the 2025 tax year, applied to one-third of the assessed value rather than the full market value. Payments come due in two installments, November 10 and April 10, with a 30-day grace period on each. Because Los Alamos is an incorporated county, a single government handles assessment, billing, and collection; there is no separate city tax office to deal with.
How Your Bill Is Calculated
New Mexico taxes only a fraction of what your home is worth. The county assessor sets the assessed value, then that figure is divided by three to produce the taxable value. The mill rate applies to the taxable value, not the full assessment.1New Mexico Compilation Commission. New Mexico Administrative Code 3.6.6 – Provisions for Imposition of Tax – Applicability – Section: Application of Tax Ratio A mill is one dollar per $1,000 of taxable value.
Here is how the math plays out for a home assessed at $450,000 at the 2025 residential rate:
- Assessed value: $450,000
- Taxable value: $450,000 ÷ 3 = $150,000
- Annual property tax: $150,000 × 0.023737 = $3,561
The 23.737 mill residential total combines levies from the state, Los Alamos County, the municipal government, the school district, and the UNM-Los Alamos branch campus.2Incorporated County of Los Alamos. Assessor FAQs The New Mexico Department of Finance and Administration recertifies these rates each year, so expect small shifts annually.3Incorporated County of Los Alamos. Certificate of Tax Rates
The 3% Cap on Annual Increases
If you own and occupy a single-family home, state law limits how fast its assessed value can grow. Under NMSA Section 7-36-21.2, the value in any tax year cannot exceed the higher of 103% of the prior year’s value or 106.1% of the value two years earlier.4Justia Law. New Mexico Statutes 7-36-21.2 – Limitation on Increases in Valuation The cap keeps your bill predictable even when the market jumps. It resets when the property changes hands, so a new buyer’s assessment reflects current market value from day one.
Exemptions That Lower the Bill
Two exemptions reduce the taxable value of residential property in Los Alamos County. Neither applies automatically. You have to file for them through the county assessor’s office.
Head-of-Family Exemption
Any New Mexico resident who qualifies as a “head of family” can take $2,000 off the taxable value of a home. The definition is wider than the name suggests: a married person (one spouse per household), a widow or widower, someone supporting a relative, or a single person living alone all qualify. Only one person per household can claim it, and only in one county per year.5Justia Law. New Mexico Statutes 7-37-4 – Head-of-Family Exemption At the current residential rate, the savings come to about $47 a year. Small, but worth claiming once and done.
Veteran Exemption
Veterans with an honorable discharge who served at least 90 continuous days of active duty, or six years in a reserve or guard component, can exempt $4,000 of taxable value. The unmarried surviving spouse of a qualifying veteran can also claim it. Veterans with a service-connected disability may qualify for additional relief, up to a full exemption on their principal residence.6New Mexico Department of Veteran Services. State Benefits Legislation introduced in the 2025 session (HB 47) proposed raising the standard veteran exemption to $10,000 for tax year 2026, so check with the Los Alamos County Assessor for the current amount before filing.
When Payment Is Due
The property tax year splits into two installments, and the deadlines are identical statewide:
- First installment due November 10, with a grace period through December 10
- Second installment due April 10, with a grace period through May 10
These dates come from NMSA Sections 7-38-38 and 7-38-49.7New Mexico Taxation and Revenue Department. Important Dates If a deadline falls on a weekend or holiday, payment is due the next business day. Miss the grace period and interest starts at 1% per month on the unpaid balance. A separate penalty of 1% per month also applies to delinquent taxes, capped at 5% of the amount owed.
Protesting Your Valuation
If the assessor’s valuation looks too high, you have a formal protest window. File a written petition with the Los Alamos County Assessor by the later of April 1 of the tax year or 30 days after the assessor mails your notice of valuation.8Justia Law. New Mexico Statutes 7-38-24 – Protesting Values Determined by County Assessor The petition has to identify the property, explain why the valuation is wrong, and state what you believe the correct value is. A timely filing gets you a hearing.
If the hearing doesn’t resolve things, there’s a second path. After your tax bill arrives and you pay it in full, you can file a claim for refund in district court. That filing must happen within 60 days of the first installment due date.9New Mexico Taxation and Revenue Department. Appeal Process Court filings cost more and move slower, so most homeowners resolve things at the assessor level.
What Happens If You Stop Paying
The escalation is predictable. Once the grace period passes, interest accrues at 1% per month and a 1% monthly civil penalty stacks on top, capped at 5% of the delinquent amount. If the taxes remain unpaid long enough, the New Mexico Taxation and Revenue Department can sell the property at public auction, with the minimum bid set to cover all delinquent taxes, penalties, interest, and costs.
New Mexico does not give former owners a right of redemption after a tax sale. You have two years to challenge the sale in court, but the property itself is gone once the gavel falls.10New Mexico Taxation and Revenue Department. Delinquent Property Tax Auctions A delinquent bill in Los Alamos compounds quickly and ends badly if ignored, so even a partial payment and a call to the assessor’s office beats silence.