If something unavoidable happens and your rent will be late, there are a few steps you can take:
If your lease says there is a penalty for late payments, expect to pay it. If you’re really short on money, ask the landlord if you can do some chores (yard work, exterior painting, odd jobs) to pay for part of the rent. Keep communicating with your landlord and be honest and realistic about your situation. Keeping the lines of communication open will go a long way towards fostering a willingness from your landlord to work with you on this problem.