Most advice on this question is useless, because it is either "get as much as you can afford" or a chart of state minimums. Neither helps you pick a number.

Here is a method instead. It takes about fifteen minutes and one phone call to your broker, and it produces an actual figure rather than a feeling.

One thing to hold onto while you work through it. UM/UIM is the only coverage on an auto policy that is bought for you. Liability, where most of the premium and nearly all of the attention goes, answers claims other people bring against you, and it pays them. UM/UIM pays you. It is the one line where the number you pick is the number you get back, which is the whole reason it is worth fifteen minutes.

Step One: Find Your Ceiling

Before you calculate what you need, understand what you are allowed to buy.

California requires your carrier to offer uninsured motorist limits equal to the bodily injury liability limits on your policy. Above the statutory minimum offer of $30,000 per person and $60,000 per accident, carriers match your liability limits, and as a matter of underwriting practice they will not write UM/UIM above that line.

So your bodily injury liability limit is the cap on your UM/UIM limit. If you want more UIM than your liability limit, you have to raise liability first. That reorders the whole exercise: you are not choosing UIM in isolation, you are choosing a liability number and then deciding whether to take the full match underneath it.

Take the full match. There is almost never a good reason not to, and the reason is in the next section.

Step Two: Understand Why Low Numbers Pay Nothing

California UIM is a difference-in-limits coverage. Your insurer pays your UIM limit minus whatever the at-fault driver's carrier already paid you. It does not stack on top of their policy.

The practical consequence is a cliff at the bottom of the range. If you carry $30,000 in UIM and you are hit by a driver carrying California's $30,000 minimum, your UIM pays zero. California defines an underinsured vehicle as one insured for less than your own UM limits, so at equal limits the coverage never triggers at all.

This got worse, quietly, on January 1, 2025. California's minimum liability limits rose to 30/60/15 from 15/30/5, where they had stood since 1967, and the minimum UM/UIM offer rose to $30,000 and $60,000 alongside them. The floor came up under everyone. A lot of Californians are now carrying UIM limits identical to what the typical minimum-limits driver carries, which means live premiums and dead coverage.

So the first rule of picking a number: it has to clear the minimum by a wide margin to do any work at all.

Step Three: Do the Income Math

This is the part nobody does, and it is the part that actually determines the right answer.

Lost earning capacity is usually the largest single component of a serious injury claim, and it scales directly with what you earn. Run two numbers:

The recoverable-injury number. Take your gross annual earnings and multiply by how long a significant orthopedic injury would keep you out. For most professionals a cervical or lumbar fusion, or a complex extremity fracture, means somewhere between six and eighteen months before you are back to full capacity. Add medical costs. A single-level fusion with the associated imaging, therapy, and follow-up regularly bills in the low-to-mid six figures before anyone negotiates it down.

Someone earning $300,000 who loses a year is looking at roughly $300,000 in wage loss, $150,000 or more in medical billing, and then general damages on top, which in California are not formulaic but are rarely smaller than the economic loss in a case involving surgery. That is a claim in the high six figures on a recoverable injury.

The permanent-impairment number. Now assume you do not get all the way back. Take the annual earnings you would lose, even a fraction, and multiply by the years to your intended retirement, then discount it. A 20% permanent reduction on $300,000 over twenty remaining working years is a seven-figure present-value loss before you add anything else.

You are not insuring the fender-bender. You are insuring the second number.

Step Four: Count the Whole Household

UM/UIM follows the person, not the vehicle. On a standard California policy it covers you and your resident relatives as pedestrians, as cyclists, as passengers in other people's cars, and in most rideshare situations.

So the limit you pick is also the limit that applies to your spouse walking to lunch, your kid biking home from practice, and you in the back of an Uber. One decision, one premium, the whole household. That usually argues for a higher number than people reach when they are imagining only themselves in their own car.

Pay attention to both figures on the line, too. A limit written as 250/500 means $250,000 per person and $500,000 for the whole accident. If two people in your car are seriously hurt, the per-accident number is the one that binds, and it is the one most people never look at.

Step Five: Ranges People Actually Land On

With the caveat that this depends on your income, assets, dependents, and what you already carry, here is roughly where the reasoning above tends to come out. These are starting points for a conversation with your broker, not legal advice about your policy.

• State minimum, 30/60. Functionally not coverage, for the reason in step two. If this is what you have, this is the finding of the exercise.
• 100/300. A real floor. Covers a moderate injury with meaningful time off. Insufficient for a professional income if the injury is permanent.
• 250/500. Where a household with professional income and a mortgage generally ought to start. Covers the recoverable-injury number in step three with room to spare.
• 500/500 or higher, plus a UM/UIM endorsement on the umbrella. What the permanent-impairment number argues for once earnings pass roughly $250,000, or where a specialized skill means the downside is loss of a career rather than loss of a year.

That last one requires a specific ask. A personal umbrella in California does not automatically extend uninsured or underinsured motorist coverage. It has to be added by endorsement, and not every carrier offers one here. Households with a $2 million umbrella and $100,000 of UIM are common, and it is a structure that only protects them when they are the one at fault.

Step Six: Get the Actual Price Before You Decide

We are not going to quote you a premium. Pricing depends on your carrier, your record, your vehicles, your territory, and your household, and an article that invents a number is not helping you.

What we will give you is the script, because a vague question gets a vague answer:

• "What are my current bodily injury liability limits and my current UM/UIM limits?"
• "Quote me UM/UIM matched to my liability limits."
• "Quote me liability at 250/500 and at 500/500, with UM/UIM matched to each."
• "Does my umbrella carry a UM/UIM endorsement? If not, can you add one, and what does it cost?"

Ask all four in one call. Then look at the delta against what you pay now and decide with real figures. In our experience the increment on UM/UIM is the least expensive meaningful improvement available on a personal auto policy, but you should verify that against your own quote rather than take our word for it.

The Part Where We Tell You Not to Call Us

Nothing in this article requires a lawyer, and nobody pays us anything when you raise your limits. This is a fifteen-minute conversation with your broker and it is worth more than any consultation we could give you today.

The reason we write about it anyway: in every serious car accident case we take, there is a moment where we pull the declarations page and learn what the ceiling is. That ceiling was set years earlier by someone who had no idea it would ever matter, and it is fixed. We can argue causation, we can prove earning capacity, we can take the claim to arbitration. We cannot argue our way above a policy limit.

Make that decision on a Tuesday afternoon with a calculator, not after a crash with a claim number.

If you want the arithmetic behind why a low UIM limit can pay literally nothing, it is worked out in detail in the piece on UIM limits and liability limits. And if you have already been hit and you are trying to work out what your policy covers, send us the declarations page. We will read it with you.