Break down the end-of-year target into monthly targets.
You'll be tracking progress vs target for each month separately, but won't keep track of the cumulative performance for the entire year. For example, if the annual target is to sell 1200 books, you could set a simple monthly target of 100 books (or adjust the monthly targets for things like seasonality).
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Set cumulative targets for the year.
Instead of breaking the yearly target into individual monthly targets, you can also set cumulative targets. If the annual target is to sell 1200 books, you can target 100 books sold for January, 200 for February, and so on. In this case, you also need to update progress cumulatively of course. This approach allows you to see the cumulative performance for the entire year.
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Only add the end-of-year target to December.
Also in this case, you'll have to update progress cumulatively. If the target is to sell 1200 books this year and you sold 100 in January and 50 in February, the actual value for January should be 100 and for February 150. This approach allows you to see the cumulative performance for the entire year.