$1,000 invested at 7% annual return compounded monthly grows to $4,039 in 20 years — $3,039 of that is compound interest. Adding $200 monthly contributions would grow the total to $108,224.

Key Numbers

• •Starting amount: $1,000
• •Value after 20 years at 7%: $4,039
• •Interest earned: $3,039
• •With $200/month added: $108,224
• •At 7%, money doubles roughly every 10.3 years (rule of 72)