Calculate the percentage increase from project units, lot area and base density, or two densities. Apply an entered bonus to base units for a pre-rounding total.
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Density Bonus Formula
The calculator uses one of four formulas depending on the inputs you have:
- Base Units – units allowed by the underlying zoning before any incentive.
- Proposed Units – total units in the project, including bonus units.
- Base Density – allowed density (units/acre, units/hectare, or units/m²).
- Built Density – proposed or as-built density on the site.
- Site Area – the program-defined site area used to compute base units.
- Bonus % – the percentage increase over base allowance.
The calculator converts density and area to compatible units before computing. Results are arithmetic estimates before statutory rounding. The governing program defines the eligible site area and how base and bonus components are rounded.
Reference Tables
The table below summarizes selected California examples from the HCD April 2026 fact sheet. Eligibility and project conditions apply; these are not universal tiers.
| Affordable / Set-aside Provision | California Bonus Example |
|---|---|
| 5% very low income | 20% |
| 10% low income | 20% |
| 10% moderate income (for-sale) | 5% |
| 15% very low income | 50% |
| 100% affordable project | 80% of lower-income base units; certain qualifying locations allow unlimited density |
| Senior housing (100%) | 20% |
| Base Units | +20% | +35% | +50% |
|---|---|---|---|
| 20 | 24 | 27 | 30 |
| 50 | 60 | 67.5 | 75 |
| 100 | 120 | 135 | 150 |
| 250 | 300 | 337.5 | 375 |
Example
Assume the applicable area is 4 acres and the base density is 20 units/acre. Base units before rounding = 20 × 4 = 80. A proposal of 100 units represents a 25% increase; this example does not determine affordable-housing eligibility.
Bonus % = ((100 − 80) / 80) × 100 = 25%. That is 20 extra units above the base allowance, or a built density of 25 units/acre.
FAQ
Does the bonus apply to fractional units? The math can produce decimals. The governing law defines rounding; California Government Code 65915(q), for example, requires separate upward rounding of fractional base and bonus components.
Is the set-aside counted from base units or total units? For the California eligibility thresholds summarized above, affordable-unit percentages use the base project before bonus units. Other programs and project types may define a different basis; check the applicable requirements.
Can the bonus stack with other incentives? Density bonuses are usually paired with concessions, waivers, or reduced parking. Those are separate from the unit count and are not included in this calculation.
What area do I use for site area? Use the area basis required by the governing program. It is not always net developable area: California base density, for example, uses the gross residential density of the project parcels.
