London in January and February is cold, grey, and wonderfully quiet. You get straight into the British Museum and the National Gallery without waiting in a line, and the corner pubs are full of locals hiding from the wind instead of tourists taking selfies. Flights and hotels drop to their lowest prices of the year during these months, making it the smartest time to go if you do not mind wearing a heavy coat.
Spreading a four-thousand-dollar trip out over several months makes the cost manageable instead of hitting your checking account all at once. You just need a clear plan for paying it back so you do not get stuck with extra costs when the bills pile up.
Remember that the intro window is a hard deadline, not free money, and any remaining balance at the end of the 15 months will start gathering standard interest.