$5,000 invested at 7% annual return compounded monthly grows to $20,194 in 20 years — $15,194 of that is compound interest. Adding $200 monthly contributions would grow the total to $124,379.

Key Numbers

• •Starting amount: $5,000
• •Value after 20 years at 7%: $20,194
• •Interest earned: $15,194
• •With $200/month added: $124,379
• •At 7%, money doubles roughly every 10.3 years (rule of 72)