Timing is everything. It's true in life and it's true for FAR.
Subscription revenue can be tricky but like anything else can be explained logically.
Sports Illustrated receives cash for magazine subscriptions that they have yet to provide. SI would debit cash and credit an unearned income account. Did they earn the money received? No. Because they did not yet mail a magazine yet. This works as a liability account because if SI is unable to send a magazine per the agreement they won't earn the money and will have to pay the cash back.
Once they mail the first issue, they Debit Unearned Income total for 1 month. Credit Revenue. Revenue is a credit balance.
Like I said, timing is important. Let's return to the prepaid expense example.
You pay for rent for the year in advance. It's an asset because the company has the prepaid rent to use for it's benefit.
Remember too that assets are listed in order of liquidity on the balance sheet. Typically, rent is paid on a monthly basis. So debit Rent Expense, Credit Prepaid Rent for the monthly amount of the total you paid in advance for a 12-month period.
I juxtaposed buying a truck with prepaid rent because they are dealt with similarly. An asset is intended to be used by the company for business-related purposes. Just like PP&E, throughout the current period you decrease the total asset amount by the amount of usage.
There are some differences of course but the mechanics (journal entries) are very similar. Prepaids are current assets because the company is expected to use up the entire benefit within a year. Conversely, the entire benefit is expected to be expired in more than one year. Generally we know for a certainty the amount to reduce the Prepaid asset. Depreciation–the mechanical equivalent of booking the monthly rent expense–is based on an estimate (eg STL vs DDB and is there a salvage value).
For each type of asset I mentioned you also “expense” the amount of the asset's benefit to the company that the company used.
As someone mentioned, that's a critical difference between an Income Statement and a Balance Sheet. An Income Statement is showing the outside what activities took place in a given period. Here, which assets did you use up? A balance sheet would be used to show, among other things, how much of said assets a company has available to use.
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So like I said, instead of merely memorizing formulas and journal entries for the sake of it, think about what you're asked to do.
The questions get tricky because you have to keep in mind how many months have gone by. The testmakers LOVE to test you on that. T-accounts can help keep everything straight.
You'll get it.