expression, godan verb (-su)
increase one's savings
A straightforward phrase meaning to grow the amount of money one has saved, often through deposits or interest.
毎月少しずつ貯金を殖やしています。
I am increasing my savings little by little every month.
貯金する means 'to save money' (the act of putting money aside), while 貯金を殖やす focuses on growing the already saved amount.
Compound of 貯金 (savings) + を (object marker) + 殖やす (to increase). The verb 殖やす is commonly used for increasing assets or numbers.