State Density Bonus Law: how much extra density your project can claim

The State Density Bonus Law, Government Code §§ 65915–65918, is the workhorse density tool for California multifamily projects of five or more units. Provide a qualifying share of affordable, senior, student or shared housing and the city must award a density increase above the maximum allowed by zoning and the general plan, plus regulatory relief. It is a state mandate: a city that has not adopted a local ordinance still has to comply.

For a small developer the bonus units themselves are often only half the value. The concessions, waivers and statutory parking caps routinely unlock more pro-forma value than the extra units — they are how a project escapes height limits, FAR caps, and parking minimums that would otherwise kill feasibility.

The base scale in § 65915(f) starts at a 20% bonus for a 5% very-low-income set-aside or 10% lower-income set-aside, and climbs on a sliding scale — a 15% very-low set-aside earns a 50% bonus. Separate tracks exist for senior housing and mobile-home parks (20% bonus), student housing (35%), moderate-income for-sale condominiums, and land donation. A 100%-affordable project earns an 80% bonus — and unlimited density if it sits within a half mile of a major transit stop.

Later amendments layered on more: § 65915.7 and § 65917.2 add enhanced local and transit-oriented bonus programs, and recent legislation (through the 2025 session, effective January 1, 2026) continues to adjust the mix — read the current text rather than a secondary summary, because the percentages and categories have changed nearly every year.

• Underwriting watch-outs:
• The bonus is calculated on maximum allowable residential density — establishing that base number (general plan vs. zoning conflicts, density ranges) is the most litigated step. HCD's technical-assistance letters treat the higher figure as controlling when documents conflict.
• Fractional units round up, at each step of the calculation.
• Affordability terms run 55 years for rental (45 for ownership) — model the covenant, not just year-one rents.

Concessions and incentives (§ 65915(d)) are cost-reducing modifications — reduced setbacks, mixed-use allowances, fee deferrals — awarded on a sliding count (one to four, and more for 100%-affordable projects). The city must grant them unless it makes written findings, supported by substantial evidence, that the concession does not reduce costs or causes a specific adverse health or safety impact.

Waivers (§ 65915(e)) are different and often more powerful: there is no numeric limit on waivers of development standards that would physically preclude the project at its bonus density. Height, FAR, open-space and lot-coverage standards are all waivable on that showing.

• Underwriting watch-outs:
• Ask for concessions and waivers in the application itself — the statute bars the city from requiring extra studies beyond reasonable eligibility documentation.
• Cities may not condition a bonus application on preparing additional reports; § 65915(a)(2)–(3) sets processing timelines tied to completeness.
• HCD has repeatedly intervened where cities tried to deny concessions — see the Danville, Los Gatos and Santa Cruz technical-assistance letters in the library.

Section 65915(p) caps what a city may require for a bonus project regardless of local code: at most one space per 0–1 bedroom unit and 1.5 spaces per 2–3 bedroom unit, inclusive of guest and accessible parking. Within a half mile of a major transit stop (with reasonable access), the city cannot require any parking for many qualifying projects, and rent-restricted senior developments with paratransit access are capped at 0.5 spaces per unit.

Because structured parking often costs $40,000–$80,000+ per stall, the parking article alone can decide feasibility on tight urban sites. Run the pro forma both ways before assuming local minimums apply.

Section 65915(c)(3) is the trap for value-add and teardown deals: no bonus, concession or waiver may be granted on a site where rental units are or were occupied by (or restricted to) lower-income households — including units vacated within the past five years and units subject to rent control — unless the project replaces those units with equivalent affordable units, in addition to the set-aside that earns the bonus.

• Underwriting watch-outs:
• Diligence the site's rental history five years back — rent rolls, rent-board registration, and vacancy records. Assume tenants unknown = lower income (the statute presumes it).
• Replacement units stack on top of the qualifying set-aside; on former rent-controlled sites the combined affordability load can exceed what the bonus is worth.
• HCD's Carlsbad replacement-unit letter in the library is the clearest agency walkthrough of this analysis.