It's every renter's worst nightmare: you're going to have to pay your rent late. Maybe you just don't have the money yet, or maybe you have it, but the check won't get to your landlord in time. Read About.com's helpful advice for trying to smooth things over with your landlord.
First, read your lease to see if there is a grace period. Usually rent is due on the first, but many leases have a grace period during which the rent is still considered on time. If you can get your rent in by the end of the grace period, congratulations, you've avoided some stress! But if there isn't a grace period or you still won't have the money, read on for what to do.
Whatever you do, DO NOT write a check that will bounce in the hopes that your landlord won't cash it right away. A check that is returned for insufficient funds will result in an angry landlord having to track you down and it will make you look like an unreliable tenant. Wait to write your rent check until your account has enough money to cover it.
Write a letter to your landlord outlining why you can't pay your rent when it is due, asking politely for an extension, promise this is a one time thing, give an exact date you will pay the rent, and offer to pay some of the rent now and the rest on the proposed date. If you've always been a good tenant, the landlord may cut you some slack this one time. It costs money and time for landlords to find new tenants if they decide to evict you.
There will most likely be a late fee, which you can find in your lease. If you have a really good relationship with your landlord, you could ask to have the fee waived, but be prepared to pay it.
Whatever your landlord agrees to, be sure to get it in writing with their signature. Then keep that in your records so they can't come back and penalize you when your rent is late. It's also a a good idea to keep it when it's time to apply for a new apartment in the future.