This really subjective on your situations depends on at what age group you're in, but most experts believe the answer is 15 %.
The most popular method in managing your finance is the 50/30/20 rules.
50 % allocated for necessities (such as housings and foods)
30% allocated for lifestyle (such as place to hang out)
20% allocated for financial related matters.
From those 20 % allocation, 15 % is advised for savings and 5% for others financial matters if you're in your 20s
