$50,000 invested at 10% annual return compounded monthly grows to $135,352 in 10 years — $85,352 of that is compound interest. Adding $200 monthly contributions would grow the total to $176,321.

Key Numbers

• •Starting amount: $50,000
• •Value after 10 years at 10%: $135,352
• •Interest earned: $85,352
• •With $200/month added: $176,321
• •At 10%, money doubles roughly every 7.2 years (rule of 72)