$10,000 invested at 7% annual return compounded monthly grows to $20,097 in 10 years — $10,097 of that is compound interest. Adding $200 monthly contributions would grow the total to $54,714.

Key Numbers

• •Starting amount: $10,000
• •Value after 10 years at 7%: $20,097
• •Interest earned: $10,097
• •With $200/month added: $54,714
• •At 7%, money doubles roughly every 10.3 years (rule of 72)