Limit the Calculated Value to a max Value - SwiftUI

Question

If Values are inserted in the app and not in the "lets say prefer order" a big value occurs, it is correct but it doesn't look good.

For example if the second Textfield (userData.Rent) is filled before the first Textfield(userData.BPrice) a value for the "return Brutto" is 24 thousand % ...

How can the calculated value be limited to a certain value, for example it cannot go higher than 20% or any other value. But below this value it moves freely.

It should more or less stop at lets say 20%

// ContentView:

struct ContentView: View {
    @EnvironmentObject var userData: UserData

    var Brutto: Double{
        let price = Double(userData.BPrice) ?? 0
        let rent = Double(userData.Rent) ?? 0

        let Brutto = rent * 12 / price * 100

        return Brutto
    }

    var body: some View {
        VStack {            
            Text ("\(Brutto, specifier: "%.1f")")
        }
        VStack{
             TextField("BPrice", text: $userData.BPrice)
               .keyboardType(.decimalPad)
         }
         VStack{
              TextField("Rent", text: $userData.Rent)
               .keyboardType(.decimalPad)
          }
    }

// UserData File:

class UserData : ObservableObject {

  private static let userDefaultBPrice = "BPrice"
  private static let userDefaultRent = "Rent"


  @Published var BuyingPrice = UserDefaults.standard.string(forKey: UserData.userDefaultBPrice) ?? "" 
  {
    didSet {
      UserDefaults.standard.set(self.BPrice, forKey: UserData.userDefaultBPrice)
    }
  }

  @Published var Rent = UserDefaults.standard.string(forKey: UserData.userDefaultRent) ?? "" {
    didSet {
      UserDefaults.standard.set(self.Rent, forKey: UserData.userDefaultRent)
    }
  }
  private var canc: AnyCancellable!

}

Thanks