No, for income tax purposes, it's not okay for you to include the first month's rent in your 2018 income since rent is taxable in the year the money is received (assuming that you are a cash basis taxpayer). You received the money in 2017.
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The Security Deposit is not income and is not taxable. You generally have to give the Security Deposit back to the tenant once they vacate the unit. If you keep all or a portion of it, you'll then claim it as income.
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