Growth · Instrument 01
Every compound-interest projection assumes the same return every year — a perfectly smooth sheet. Reality is a jagged thread. Build your terrain from the rates you'd assume, then weave the real S&P 500, bonds, inflation, gold and silver through it and watch where the market dives under your sheet and where it bursts back through. Drag the scene to see it from every side.
This browser can't render the 3D terrain, but every path still computes — see the result cards below.
Left to right is time. Up is your balance. Each rate you switch on becomes a full translucent sheet — a bent piece of paper spanning the whole floor, curling upward at exactly the pace that rate compounds. Turn on several and they fan above one another; because each sheet is see-through, the overlaps stay legible instead of hiding each other.
The bright jagged threads are real history: the actual year-by-year path of each asset, beaded at every year-end. This is where the picture earns its keep. Follow the S&P thread against your 7% sheet — it dives below the paper in 2000–2002, punches through it in the recovery, plunges under again in 2008, then climbs clean out the top. Same neighborhood as the smooth assumption over the long run, nothing like the same ride. The gap between thread and sheet at any moment is the part every smooth projection quietly hides — and why the order of good and bad years matters as much as the average.
The inflation thread is the floor that matters most: the balance your contributions would reach merely keeping pace with prices. Any thread or sheet running below it is losing purchasing power. Gold and silver show how differently hard assets travel — silver especially lurches, a reminder that a decent average return can hide a brutal path.
The tool compounds your rate sheets at the frequency you choose (yearly by default) and adds contributions at the end of each month; historical series apply each year’s actual return across that year. Outputs are nominal and pre-tax — arithmetic, not advice.
Interest earned on both your original principal and on previously earned interest. Each period's gains join the base that earns the next period's gains, which is why the curves bend upward instead of rising in a straight line.
A formula assumes the same return every single year; markets never cooperate. The S&P 500 has had many losing years scattered among the winners, so the real path is jagged. The long-run average can still be attractive, but the ride is bumpy and the sequence of good and bad years matters.
Far more than intuition suggests. Over 30 years, $10,000 grows to roughly $33,000 at 4% but roughly $198,000 at 10% with monthly compounding. A rate 2.5× higher produces a balance roughly 6× larger — and the gap widens every additional year.
Broad stock returns have historically averaged roughly 7–10% per year before inflation, but the past guarantees nothing. Many planners model 6–7% to be conservative. Overlaying your assumption on the real historical paths is more honest than trusting one smooth number.