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Rent increases are never, ever fun. Every year, I hold my breath when it's time to renew my lease in the hopes that the hike is still within my budget, especially because I love where I live. Fortunately my landlords have always played fair. But let's be frank -- some don't. And when that happens it leaves many tenants wondering: What are the rules on raising rent, anyway?

Read on for answers to the questions that keep renters up at night.

How often can landlords raise rent?

Landlords can't just raise your rent whenever they feel like it; they have to wait until whatever contract you've signed with them expires, says Robert Pellegrini, president of PK Boston, a real estate and collections law firm with offices in the Greater Boston area. That means if you have a lease, they can't raise it until the term expires. So if you've signed a one-year contract, it'll be a year before rent can go up, or two years if you've signed a two-year lease (which is why signing a lease for two years or longer is wise to keep down rent). Or if you're renting month to month, your rent can't go up until the end of any given month. Simple rules. But real rules.

How much notice should renters receive of an increase?

In most states, landlords are legally required to give tenants at least 30 days notice of a rent increase, although that can vary based on how high it's hiked. In California, for instance, that advance notice expands to 60 days if the increase amounts to more than 10% of the rent.

These rules are also typically true for a "tenant at will" (i.e., you do not have a lease) and (more surprisingly) a tenant in a rooming house, who likely pays rent weekly.

"In this case, one would assume that seven days' notice would suffice. Not the case!" says Pellegrini. "Tenants in rooming houses still require 30 days' notice for a rent increase."

How much can landlords legally hike what renters pay?

"When it comes to how much a landlord can raise rent, anything flies," says Pellegrini. "There are no rules, and it's totally at their discretion." Except, of course, if you're living in a rent-stabilized or rent-controlled apartment, in which case there are strict government provisions in place as to how much rent can be raised (or if it can be increased at all). Finding one of these apartments is sort of like locating the Holy Grail, however, so if you don't know if you have a rent-regulated apartment, chances are you do not.

And if that's the case, you're mostly at the mercy of your landlord and the rental market in your area when it comes to rent pricing. A landlord who raises the rent to punish a renter is definitely on the wrong side of the law.

"If it looked to a judge like the landlord was raising rent punitively -- say, for example, to get 'payback' for the tenant contacting the Board of Health for a health code violation -- then this is not OK, and the landlord could be found guilty and made to pay as much as triple damages and court costs," says Pellegrini.

Can a landlord raise rent retroactively?

The short answer is no. In most cases, if a landlord has slapped a tenant with a retroactive rent increase, he was negligent in letting the tenant know about it at the appropriate time.

"Often, a landlord provides notice of the increased rent retroactively together to try to bully renters out, knowing that the tenant might be overwhelmed due to the 'back rent' and would be more likely to vacate," says Pellegrini. If this is the case for you, be aware that a tenant can file suit against a landlord, or simply counterclaim if an eviction has already been initiated by the landlord.

What should renters do if they think their landlord illegally raised the rent?

"A tenant should keep track of every correspondence they receive," says Pellegrini. "They should also take notes when communication is verbal, and keep track of the dates of each communication." This is especially important when trying to prove harassment (to pay rent or otherwise).

But don't assume that your landlord is automatically the bad guy.

"In my opinion, the vast majority of landlords do the right thing, and, out of the slim percentage that do not, they aren't even aware that they did something incorrectly," says Pellegrini. "So, in all but a few cases, I'd highly recommend that the tenant communicate with the landlord first if something doesn't seem right. If the tenant ends up in court, or starts things off in a threatening way, they should remember that the landlord owns the property. And, if the landlord finds the tenant to be difficult to work with, the landlord is entitled to allow the tenancy to expire and find a new tenant."

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