Almost every week now somebody asks me about renting out an ADU in San Diego — usually a homeowner with a finished granny flat out back, or one halfway through permitting, wondering what it will actually put in their pocket. The gross number is easy to find. The net number is the one nobody sends them.
So here it is. On an illustrative detached San Diego ADU renting at $2,450, an owner nets somewhere around $1,525 a month after vacancy, management, utilities, maintenance, insurance and — the line everyone forgets — the property tax increase the ADU itself triggers.
Key takeaways
- A detached San Diego ADU commonly rents between $1,800 and $2,900 depending on size, neighborhood and whether it has its own yard and parking.
- Building it triggers a partial property tax reassessment on the new construction only — roughly $3,300 a year on a $275,000 build. Prop 13 protects the rest of your parcel.
- ADUs in the City of San Diego are long-term rentals. Under 31 nights puts you into short-term rental licensing territory, and ADUs generally are not eligible.
- A garage conversion at roughly $150,000 usually beats a $275,000 new-build ADU on return, even at lower rent.
- Separate metering, a separate lease, and separate screening. Treating the ADU as “part of the house” is how owners end up with a problem they cannot unwind.
Who this is for
San Diego owners with an ADU already built, under construction, or seriously penciled — the Normal Heights garage conversion, the North Park backyard studio, the Clairemont junior unit carved out of an oversized primary bedroom. You are not trying to become a landlord for a living. You are trying to make one property carry more weight.
I get the appeal, and I am not going to talk you out of it. But I do want you to walk in with the honest number rather than the Instagram number, because the gap between them is usually about $900 a month.
The rules, briefly, before the math
The City of San Diego adopted a set of ADU program reforms this year that touched fees, fire-access requirements, parking and how the density bonus program defines walkability to transit. If your unit is already permitted and finished, none of that changes your rental. If you are still in design, it matters a great deal — start at the city’s Accessory Dwelling Units page and confirm current requirements before you finalize anything.
Three things that hold true regardless:
- You cannot sell it separately. An ADU is part of your parcel. It adds value and income, not a second deed.
- It is a long-term rental. Rentals under 31 consecutive nights fall under the city’s short-term ordinance, and ADUs generally are not eligible for those licenses. I laid out that whole framework in San Diego short-term rental rules in 2026.
- It is a real tenancy. California habitability standards, deposit rules and notice requirements apply exactly as they would to any other unit, whether or not the tenant is thirty feet from your kitchen window.
What an ADU actually nets
Here is a 600-square-foot detached one-bedroom, built for $275,000, rented at $2,450. For context, county average asking rent across all unit types was around $2,453 with vacancy near 5.5% in Kidder Mathews’ Q2 2026 multifamily report — so a well-finished ADU rents right at market for a small unit, not below it.
| Line | Annual | Note |
|---|---|---|
| Gross rent | $29,400 | $2,450 × 12 |
| Vacancy at 5.5% | −$1,617 | County vacancy, Q2 2026 |
| Management at 10% | −$2,778 | Small units price higher than large ones |
| Utilities | −$1,800 | $150/mo if not separately metered |
| Maintenance and turnover reserve | −$1,200 | New construction; budget more as it ages |
| Insurance increase | −$400 | Added structure and landlord coverage |
| Property tax on the new construction | −$3,300 | ~1.2% of $275,000 added assessed value |
| Net | $18,305 | About $1,525/mo — a 6.7% return on build cost |
The property tax line is the one that surprises people. Building an ADU does not reassess your whole parcel — Prop 13 protects your existing base year value — but the new construction gets its own assessment added on top. That is permanent, and it is roughly two weeks of rent every year.
Why a garage conversion usually wins
Run the same math on a 400-square-foot garage conversion. Build cost around $150,000, rent around $1,950. After the same categories — and a smaller tax add because the added assessed value is smaller — you land near $13,600 net, or about 9.1% on cost.
Lower rent. Better return. That is the pattern I see over and over, and it is why my first question is never “how big can we build” but “what do you already have that has walls and a roof.”
The rent-cap question, because it is the one that bites
California’s statewide rent cap and just-cause rules do not apply uniformly to ADUs. Whether yours is covered depends on the underlying property type, whether the owner is an individual or an entity, whether you occupy the primary residence, and whether you delivered the required exemption notice in the lease. Those details decide whether you can raise rent 12% next year or 8.2%.
I walked through the framework in how much a San Diego landlord can raise rent in 2026. Do not guess on this one, and do not let a template lease off the internet decide it for you.
Five things I tell every ADU owner before the first listing
- Meter it separately if you possibly can. $150 a month of shared utilities is $1,800 a year, and shared meters create disputes that are genuinely unwinnable.
- Write a real lease, not a handshake. Proximity is not a substitute for terms. Especially if the tenant is a relative or a friend of one.
- Screen exactly the way you would for a detached rental. Maybe more carefully, since this person will be in your backyard — my process is in tenant screening in San Diego.
- Define the physical boundaries in writing. Parking space, trash bins, laundry access, yard use, the gate. Every ADU dispute I have mediated started with an assumption nobody wrote down.
- Call your insurance agent before the tenant moves in, not after. A homeowner’s policy covering an owner-occupied residence is not the same policy you need with a paying tenant on the parcel.
Frequently asked questions
How much can I rent an ADU for in San Diego?
Most detached one-bedroom ADUs we see land between $1,800 and $2,900 a month depending on neighborhood, size, parking, private outdoor space and finish level. Coastal and central neighborhoods sit at the top of that range; inland and no-parking units at the bottom. A comparable-rent pull on your specific block beats any range I can print here.
Will building an ADU reassess my whole property?
No. Under Prop 13 your existing base year value is protected. The Assessor adds a supplemental assessment for the new construction only, at that construction’s market value. Confirm the treatment of your specific project with the County Assessor.
Can I rent my ADU on Airbnb?
In the City of San Diego, rentals of fewer than 31 consecutive nights require a short-term residential occupancy license, and ADUs generally are not eligible. Plan on a long-term or mid-term tenancy, and verify current city rules before you list anywhere.
Should I rent it furnished?
Sometimes. Small units near hospitals, bases or major employers do well as furnished mid-term rentals at 31 nights and up. It pays only if you keep it near-continuously occupied — the same conclusion I reached on full units, and the arithmetic is in the short-term rental article above.
Want the real number on your ADU?
Send me your address, the unit size, and whether it has dedicated parking. I will pull actual comparable ADU rents from your neighborhood and build the net sheet above with your numbers in it — including the tax line. Free, no obligation, and if the honest answer is “rent it to family and stop doing spreadsheets,” I will say that too.
Amara Berg — San Diego real estate and property management with Big Returns. I help owners sell for more and hold smarter, and I would rather hand you an honest net sheet than a flattering one.
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This article is general information for San Diego property owners, not legal, tax, or investment advice. ADU regulations, permitting requirements, fees, assessment practices, and state tenant-protection rules change and vary by parcel, zoning, and ownership structure — verify your specific situation with the City of San Diego, the County Assessor, and qualified counsel before building or leasing. All income, cost, and tax figures are illustrative and are not projections or guarantees. Amara Berg, CA DRE #01961620. Big Returns, CA DRE #02322119. Equal Housing Opportunity.