$50,000 invested at 7% annual return compounded monthly grows to $100,483 in 10 years — $50,483 of that is compound interest. Adding $200 monthly contributions would grow the total to $135,100.

Key Numbers

• •Starting amount: $50,000
• •Value after 10 years at 7%: $100,483
• •Interest earned: $50,483
• •With $200/month added: $135,100
• •At 7%, money doubles roughly every 10.3 years (rule of 72)