A purchase fits a spending plan only if you account for the costs that come with using it.
For a new laptop, the full cost might include a required accessory, delivery, setup or an ongoing subscription. List the expected upfront and recurring amounts separately. Compare alternatives over the same period and use the price you can confirm at checkout.
Add the likely purchase date and the amount you have already saved. This makes it easier to see whether the purchase belongs in the current month or needs a separate savings goal. Update the comparison if your requirements change.
Further reading: CFPB monthly budget worksheet.