Compound interest calculator
One lump sum, left alone. The grey line is what simple interest would give you; the green curve is compounding — interest earning interest. The gap between them is the whole argument for starting early. Hover the graph (or tap on mobile) to read both values — and the gap — at any year.
You end with
—
Interest earned
—
Vs simple interest
—
Compound
Simple interest
What this teaches
A single amount doesn’t grow in a straight line — it curves upward, because each year’s interest starts earning its own interest. That curve is compounding, and time is what bends it.