$50,000 invested at 10% annual return compounded monthly grows to $366,404 in 20 years — $316,404 of that is compound interest. Adding $200 monthly contributions would grow the total to $518,277.

Key Numbers

• •Starting amount: $50,000
• •Value after 20 years at 10%: $366,404
• •Interest earned: $316,404
• •With $200/month added: $518,277
• •At 10%, money doubles roughly every 7.2 years (rule of 72)