Can a New York landlord increase rent retroactively?
No. A rent increase in New York only takes effect on or after the effective date stated in the notice, and only if the advance notice period was met (New York uses a tenure-based notice ladder at RPL 226-c: 30 days for tenancies under 1 year, 60 days for 1-2 years, 90 days for 2+ years. Only triggers if the increase exceeds 5% or the landlord does not renew. Good Cause Eviction (Part HH 2024) caps increases at CPI + 5% or 10% max in NYC and opt-in municipalities, with exemptions for small owner-occupied buildings and new construction.). A landlord cannot demand back-dated rent at a higher rate for past months. Doing so makes the increase void as to the back-dated period. The tenant continues to owe the original rent for any month already in progress when the notice was served.
Source: RPL 226-c (HSTPA 2019)
This is an informational answer based on RPL 226-c (HSTPA 2019) as of early 2026. It is not legal advice. Housing law changes year to year and local ordinances (especially in rent-controlled or rent-stabilized cities) can override or add to state law. For contested cases, consult a New York-licensed attorney.