$10,000 invested at 10% annual return compounded monthly grows to $27,070 in 10 years — $17,070 of that is compound interest. Adding $200 monthly contributions would grow the total to $68,039.

Key Numbers

• •Starting amount: $10,000
• •Value after 10 years at 10%: $27,070
• •Interest earned: $17,070
• •With $200/month added: $68,039
• •At 10%, money doubles roughly every 7.2 years (rule of 72)