The break-even instrument · illustrative until the county releases its data

What keeps the budget whole?

Hold school services constant and the problem is one line of math: revenue growth must match cost growth. This instrument lets you mix the four dials — turnover, new units, aid, and the cost line — and see what it actually takes. Every assumption is a slider; defaults are the validated Rockville Centre figures.

cost growth ≤ levy share × (cap + physical base growth δ) + aid share × aid growth + other

Dials — district finances

Cost growth (services held constant)

Driver: health +10% on ~$20M ≈ +1.4% of budget alone (source)

Levy cap (allowable growth)

Lesser of 2% or CPI; 2026-27 final ≈2.1%

State aid growth

2026-27: ~1% on ~15% of revenue

District taxable full value

ASSUMPTION — pending DTF school-district full-value table

Dials — housing

Senior→family transitions / yr

Illustrative only: 3% to 5% a year of 2,081 senior-owned homes (ACS 2020-24) is roughly 60 to 100 moves. No measured RVC turnover rate exists; see the county ask below

Renovation per transition

Physical improvement → DTF quantity change

New units built / yr (ADU · condo)

Right-size supply near the LIRR

Avg full value per new unit

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Structural gap / yr at your cost line (before housing dials)

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Physical base growth δ required to close it inside the cap

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Construction $ / yr that δ implies on your full-value base

What your housing dials deliver—

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Data needed to make this real — the county ask

§467 / Enhanced STAR counts and exempted value by school district (Nassau Dept. of Assessment) — sizes the burden-shift and the eligible-senior pool.
DTF school-district full value for RVC UFSD — replaces the $-base assumption above.
A measured senior turnover rate for RVC (Nassau Dept. of Assessment or county recording data), to replace the illustrative 3% to 5% attrition band on the housing dial above, which has no measured rate behind it.
A district facilities/capacity study — converts "~7% enrollment decline" into actual absorbable seats and marginal cost.

Assumptions, stated: revenue mix 78% levy / 15% aid / 7% other (validated 2025-26: $109.24M levy on $139.89M budget); "other" held flat; δ (the DTF tax-base growth factor) counts only physical change — construction and renovation, never price appreciation; renovations assumed to assess at cost; new units add full value at the slider price; budget base $141.3M (2026-27 adopted). Recent reality check: the 2026-27 adopted budget grew +1.03%, and the gap was closed with a net reduction of 50.2 positions (our sum of the LI Herald figures, ledger), which is exactly the outcome this instrument prices the alternative to. Mechanics write-up: /fiscal-math · worked example: docs/BREAKEVEN_SAMPLE.md.