$1,000 invested at 7% annual return compounded monthly grows to $2,010 in 10 years — $1,010 of that is compound interest. Adding $200 monthly contributions would grow the total to $36,627.

Key Numbers

• •Starting amount: $1,000
• •Value after 10 years at 7%: $2,010
• •Interest earned: $1,010
• •With $200/month added: $36,627
• •At 7%, money doubles roughly every 10.3 years (rule of 72)