$50,000 invested at 7% annual return compounded monthly grows to $405,825 in 30 years — $355,825 of that is compound interest. Adding $200 monthly contributions would grow the total to $649,819.

Key Numbers

• •Starting amount: $50,000
• •Value after 30 years at 7%: $405,825
• •Interest earned: $355,825
• •With $200/month added: $649,819
• •At 7%, money doubles roughly every 10.3 years (rule of 72)