$50,000 invested at 10% annual return compounded monthly grows to $991,870 in 30 years — $941,870 of that is compound interest. Adding $200 monthly contributions would grow the total to $1,443,968.

Key Numbers

• •Starting amount: $50,000
• •Value after 30 years at 10%: $991,870
• •Interest earned: $941,870
• •With $200/month added: $1,443,968
• •At 10%, money doubles roughly every 7.2 years (rule of 72)