Calculate present value, future value, annuities, and perpetuities with visual timeline diagrams of cash flows.
Enter the cash flows you know - a lump sum, a repeating payment, or both - and the tool returns the missing quantity: the present value or future value of a lump sum, an annuity, or a perpetuity. Alongside the answer it draws a timeline diagram with an arrow at every cash-flow date, so the direction and timing of each payment is visible. The error users make most often is mismatched units - a monthly payment schedule with an annual interest rate, which inflates the result. Payments are assumed to land at the end of each period unless you switch to an annuity due.
A concrete input and expected output from the current implementation.
Input
present value 1000, rate 5% per year, 10 years - solve for future value
Expected output
Future value: $1,628.89. The timeline shows $1,000 at year 0 and $1,628.89 at year 10.
The balance grows by 5% of itself each year, so the future value is 1000 x (1.05)^10 = 1,628.8946, rounded to $1,628.89. The result exceeds a flat $500 gain (10 years at 5% of the original principal) because interest earns interest.
One payment grows or shrinks by the factor (1 + r) for each period: a single sum valued n periods ahead is PV x (1 + r)^n, and the same sum discounted back is FV / (1 + r)^n. A stream of equal payments is valued period by period and summed - an ordinary annuity is the finite case, a perpetuity the case where the stream never ends. The diagram draws every flow at its own date.
Every calculation produces a horizontal timeline with one arrow per cash-flow date: money coming in points one way, money going out points the other, so the sign of each flow is visible before you read the number. Payments are placed at the end of each period, the ordinary-annuity convention. Moving a payment one period earlier changes its value by exactly one period of interest.
For a fixed present value, yes: each period earns more interest, so the future value rises. The same rate pushes the other way for present value - a higher discount rate lowers the present value of a future payment, because receiving it today means giving up more growth. A perpetuity is the extreme case: its value is the payment divided by the rate, so a small rate change moves it a lot.
It can if it solves for the number of periods: enter the present value, twice that as the future value, and the rate, and the missing period count is the answer. As a rough check, the rule of 72 divides 72 by the annual rate in percent to estimate doubling time in years, and it is closest to exact near 8%.
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