How to create a Leveling System that requires more exp as you level and scaling that with a GUI?

Background: I'm making a leveling system that once you level up, the exp you needs increases. So for instance. Level 1 = 200 EXP Needed Level 2 = 400 EXP Needed.

I'm also trying to scale this with a GUI. So the GUI's bar would be 0/200 and would increase all the way to end of the bar, and then level up and go back to the beginning.

Question Is there any way to do this? I can only make it where once the EXP reaches the end of the bar, it levels you up, but the EXP needed doesn't increase. If I decided to make the EXP increase, I would have to make the bar longer.

So my theory was to reduce the EXP you get as you level up, but that isn't exact;y a good method.

-- My Method
--EXP Changing function

PlayerExp.Changed:Connect(function()
    EXP.Size = UDim2.new(PlayerExp.Value/EXPNeeded,0,1,0)
    print(EXP)
end)

--Level up function, Inside a ServerScript (RemoteEvent)
if EXP.Size.X.Offset >= EXPNeeded then
    Player.CharacterSave.Level.Value = Player.CharacterSave.Level.Value + 1
    EXP.Size = UDim2.new(0,1,0,1)
    PlayerEXP = (EXP/1.2) -- Reduces EXP as you level
end