$50,000 invested at 7% annual return compounded monthly grows to $201,937 in 20 years — $151,937 of that is compound interest. Adding $200 monthly contributions would grow the total to $306,122.

Key Numbers

• •Starting amount: $50,000
• •Value after 20 years at 7%: $201,937
• •Interest earned: $151,937
• •With $200/month added: $306,122
• •At 7%, money doubles roughly every 10.3 years (rule of 72)