$1,000 invested at 10% annual return compounded monthly grows to $19,837 in 30 years — $18,837 of that is compound interest. Adding $200 monthly contributions would grow the total to $471,935.

Key Numbers

• •Starting amount: $1,000
• •Value after 30 years at 10%: $19,837
• •Interest earned: $18,837
• •With $200/month added: $471,935
• •At 10%, money doubles roughly every 7.2 years (rule of 72)