Formulas are easier to believe with numbers attached. Each scenario below was computed by the same engine as the main calculator — change any of them there and watch the balance move.
Start with $5,000.00, assume 7% per year compounded monthly, add $100.00 at the end of each month, wait 40 years. The balance reaches $344,038.40 — of which $48,000.00 was deposited along the way and $291,038.40 (84.6% of the total) is interest.
A small start at a young age, left alone for four decades. Time does most of the work.
Start with $5,000.00, assume 7% per year compounded monthly, add $400.00 at the end of each month, wait 20 years. The balance reaches $228,564.36 — of which $96,000.00 was deposited along the way and $127,564.36 (55.8% of the total) is interest.
The same rate and start, half the time, four times the monthly deposit — and a lower finish. The two scenarios use identical assumptions; only time and deposits differ.
Start with $25,000.00, assume 2% per year compounded monthly, add $0.00 at the end of each month, wait 15 years. The balance reaches $33,738.04 — of which $0.00 was deposited along the way and $8,738.04 (25.9% of the total) is interest.
A low steady rate barely outruns its own starting line over 15 years — the clearest illustration of why the assumed rate matters.
Start with $0.00, assume 5% per year compounded monthly, add $150.00 at the end of each month, wait 30 years. The balance reaches $124,838.80 — of which $54,000.00 was deposited along the way and $70,838.80 (56.7% of the total) is interest.
Nothing to begin with. Everything in the "deposits" column was paid in month by month; everything beyond it is compounding.
Because growth is exponential in time but only linear in deposits. Doubling the years squares the compounding effect; doubling deposits merely doubles their contribution. The deposit-heavy scenario pays in far more cash and still finishes behind.
No. They are arithmetic under fixed assumptions — a way to see the shape of compound growth. Real saving and investing involve changing rates, taxes, fees and your own behaviour.
Yes — the compound interest calculator takes any combination, and the savings goal calculator solves for the deposit a target requires.