Free tools
Calculators that cite their source
Free, no signup. Three of these run on state law we read against the statute ourselves — so every answer comes with the section behind it and a link to the wording, rather than a number you have to trust.
Can I charge this?
Is my late fee legal?
Tests a fee against both things that can void it: your state's cap and its mandatory grace period. 18 states cap the amount, 15 require a grace period.
When must this be back?
Deposit return deadline
A move-out date in, the statutory deadline out — plus the condition in your state that decides when the clock actually starts. All 51 jurisdictions.
When must I serve it?
Rent increase notice
Counts backwards from the date you want the new rent to begin, which is how the question actually arises. 49 jurisdictions verified.
What is owed for a part month?
Prorated rent
Rent for a partial month on all three bases in common use, side by side, because the difference between them is what tenants query.
Why these show their working
Most calculators for these questions give you a number and nothing else, which is a problem on a subject where the numbers in circulation are frequently wrong. When we read all 51 jurisdictions against their statutes we found a Kentucky deposit deadline that does not exist, a South Dakota one published as 14 days when the statute says 21, and late-fee caps for nine states that actually come from their self-service storage law rather than landlord–tenant law.
So each answer here names the section it came from and links to a page quoting it. If you are about to put a figure in a lease or a letter, you can check it first.
The same data drives the state guides and the product itself, so a warning inside the app, a page on this site and these tools cannot tell you three different things.
General information, not legal advice. Statutes change and city ordinances can impose more than the state does — verify before relying on any figure, and each tool links to its source so you can.