Visualise Compound Interest on My Monthly Contributions

Compounding is hard to feel until you watch the numbers run. You give a starting lump sum, a monthly amount, a horizon and an assumed return; this produces a year-by-year table of portfolio value, total contributions and growth, the final figure, and how much an extra few pounds a month changes the ending. For investors who want to see the projection rather than be told it is big.

I plan to invest £{MONTHLY_AMOUNT} every month for {YEARS} years, starting with an initial lump sum of £{INITIAL_AMOUNT}. Assume an average annual return of {RETURN_RATE}% and that returns are reinvested. Show me: (1) a year-by-year table of portfolio value, total contributions, and total growth, (2) the final portfolio value at year {YEARS}, (3) how the outcome changes if I increase my monthly contribution by £{EXTRA} from year {BOOST_YEAR} onwards. Explain the maths behind compounding in plain English and highlight the point at which investment growth overtakes my contributions.