When Is The Best Time To Purchase A Laptop

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I am looking into buying a laptop for my son and I would like to know what is the best time of year to purchase it.he will be 13 in October and we plan on purchasing one around then.however, how long should he hold out for his ideal purchase?what are some things that you can look at when deciding between either a desktop or a laptop as well as the price range of those two options.can someone give me their opinion on which way is betteror roughly how much they payed for theirs?thank you so much!