Combine a starting lump sum with an optional monthly contribution to see your projected balance, total contributed, and total growth.
Future value answers one question: what does today's money, plus everything you plan to add to it, become after compounding for a stated time at a stated rate? On this page’s own defaults — $10,000 today, $200 added every month, 7% annual return, 20 years — the answer is $144,573.
Two separate mechanisms are stacked to get there. The formula is FV = PV(1+i)n + PMT × [((1+i)n − 1) ÷ i] — the first term is your lump sum compounding alone, the second is the running total of every monthly contribution compounding from the month it was made. Split apart, the $10,000 alone would grow to $40,387 over 20 years; the $200-a-month contributions alone, with no starting balance at all, would grow to $104,185. The two combine to the full $144,573 because compound growth is additive across separate cash flows.
Across 20 years you contribute your original $10,000 plus 240 payments of $200 — $58,000 in total. The remaining $86,573, just under 60% of the final balance, is growth that nobody deposited. That ratio is the entire case for starting early: the longer the horizon, the smaller the share of the ending balance that is actually your own money, and the larger the share that is compounding doing the work unattended.
A lump sum alone compounds along a smooth exponential curve from day one. Regular contributions add a second curve underneath it that starts small and accelerates, because each contribution only begins compounding from the moment it is made — a payment made in year 19 has had almost no time to grow, while the very first payment has had the full 20 years. Together, the combined curve is flattest early and steepest in its final years, which is why the value of an early contribution so heavily outweighs an identical contribution made near the end.
Nothing else in the formula is uncertain — the amounts and the time horizon are choices you make. The rate is a forecast, and small changes in it move the ending balance by far more than intuition suggests, precisely because it is compounding for 20 years rather than one. Run this calculator at 5%, 7% and 9% for the same contributions before treating any single projection as a plan rather than a scenario — the spread between the low and high case is normally the most useful output the tool produces.
The two tools solve for the same underlying mathematics; they differ only in which quantity is fixed. The compound interest calculator is built around a single deposit growing on its own, which is the first of the two terms in this page's formula. This page is built for the more common real case — an opening balance plus an ongoing habit of contributing — which is why its formula carries a second term the other tool does not need. If you are not making regular contributions, both tools give an identical answer for the lump sum alone.
Future value (FV) is what a sum of money today — plus any regular contributions you add along the way — grows to by a future date, once you apply an assumed annual rate of return and let compounding work over the full period. It's the mirror image of present value, which instead discounts a future amount back to today; see the Present Value Calculator, a companion tool, for that direction.
A lump sum alone only compounds on the money you start with. Regular monthly contributions add fresh principal every month, and each new contribution then gets its own remaining years to compound. Over long horizons this matters a lot — consistent contributions can end up producing more total growth than the original lump sum did, especially when the lump sum is modest relative to the monthly amount and the time horizon is long.
There's no guaranteed number to plug in. A diversified stock/bond portfolio has historically returned roughly 5-8% annually over long multi-decade periods (before inflation and fees), while a savings account or CD might return far less but with far less risk. It's worth running the calculator at a few different rates — say 5%, 7%, and 9% — to see how sensitive your final number actually is to the assumption, rather than anchoring on a single optimistic figure.
The underlying math is functionally the same — both grow a starting principal plus periodic contributions at a compounding rate. This tool is framed around total future value and splits the result into total contributed vs. total growth; the Compound Interest Calculator presents a similar breakdown with its own layout, so it's worth comparing both if you want to double-check a number or prefer one tool's presentation over the other.
Worked example: starting with a $10,000 lump sum, contributing $200/month, at a 7% annual return for 20 years: future value comes out to roughly $144,573. Total contributed over that time is $10,000 + ($200 × 240 months) = $58,000, meaning growth alone accounts for the remaining $86,573 — nearly 60% of the final balance came purely from compounding, not from money you put in.
This page is a single-purpose version of a broader five-variable equation — solve for present value, payment, rate, or time instead of future value on the Finance Calculator (TVM).