What £50,000 means for your stamp duty bill
At £50,000 you fall entirely within the nil-rate band, so there is no stamp duty to pay at all. The nil-rate band covers the first £125,000 of any residential purchase, and because your price sits below that threshold none of the higher rates are triggered.
You may still need to file an SDLT return even though the tax is nil. HMRC requires a return for most notifiable transactions, and the threshold for notification is lower than the threshold for paying. Purchases under £40,000 are generally not notifiable at all. Your conveyancer will confirm which applies.
For context, £50,000 is about 83% below the UK average house price of roughly £290,000. Your marginal rate at this price is 0%, meaning that is the rate charged on the next pound you add to the purchase price.