How to read the investment growth calculator

Project a saving plan forward, or turn the same projection around to solve for the starting amount, monthly contribution, return, or time a future goal would require.

What it calculates

The calculator follows a starting investment and any deposits or withdrawals month by month. It applies the return, compounding, contribution timing, contribution increases, and fees you choose, then reports the balance and the parts that produced it.

In Final balance mode the inputs determine the ending value. In the other modes the calculator repeats its monthly state transitions to find the one unknown that reaches the goal. A solved plan must both fund every fixed scheduled withdrawal and reach the requested ending balance; any amount the projected account cannot pay is reported as an unmet withdrawal.

Questions it answers

Choose What should be calculated to decide which value becomes the answer. Every other visible field remains an input.

Final balance

“What could this plan be worth at the end?” The starting investment, monthly contribution, return, and years are all inputs. An optional goal is only a reference; it does not change the projection.

Starting investment

“What lump sum would I need today?” The goal, monthly contribution, return, and time are fixed. If later deposits can reach the goal without a starting sum, the answer is nothing needed rather than a negative investment.

Monthly contribution

“How much would I need to add each month?” The solver holds the starting sum, return, time, and goal fixed. The displayed whole-dollar amount is rounded up so following it reaches rather than narrowly misses the goal.

Return percentage

“What yearly return would this plan need?” Treat the answer as a feasibility test against a realistic investment and its risks, fees, and taxes—not as a return to expect. If deposits alone reach the goal, no growth is needed.

Time to goal

“When would the balance first reach the goal?” The answer is the first crossing, to the month. If the plan does not reach the goal inside the calculator's 100-year search horizon, it reports that instead of extrapolating forever.

Major inputs

Starting investment: The amount already invested on day one. It is separate from later contributions when the result divides your money from investment growth.
Monthly contribution: The regular amount added each month. Advanced options decide whether it arrives at the start or end of the month and whether it rises each year.
Expected return: The steady annual growth assumption before inflation and tax. The calculator applies the separate fee you enter, but it does not deduct tax. A higher assumed return raises the projection but normally requires accepting more uncertainty or risk.
Years invested: How long the starting balance and contributions can compound. In Time to goal mode the exact month is the answer and the disabled year field rounds up for display.
Goal amount: A nominal amount in future dollars. A $1 million goal means $1 million when reached; it is not automatically adjusted to preserve $1 million of today's purchasing power.
Inflation: Used to restate a future balance in today's purchasing power. It does not change the nominal projection or inflate the goal.
Fees and compounding: An annual balance fee reduces what remains to compound. The compounding choice controls how often the quoted return is credited; compare products using rates and fee definitions on the same basis.
Extra cash flows: Optional recurring or one-time deposits and withdrawals are placed on the schedule you enter. Fixed withdrawals are solver constraints: a starting-balance, contribution, or return answer is not accepted unless the scheduled amounts can be paid.

What the results mean

Final or projected balance: The nominal dollars in the account at the stated time: starting money, net cash flows, and modeled growth together.
Money contributed: The deposits you supplied during the projection. Read it with the starting investment to understand how much of the ending balance came from your own money.
Investment growth: The ending balance minus the starting investment and deposits, with completed withdrawals added back. This isolates market gain or loss; withdrawals and unmet withdrawals are shown separately. Tax is not deducted.
In today's money: The future balance discounted by your inflation assumption. It is an estimate of purchasing power, using the constant-dollar idea explained by the U.S. Bureau of Labor Statistics.
Required amount or return: The minimum modeled input that reaches the goal under the other assumptions. A required return that looks implausibly high is usually a signal to save more, allow more time, or revise the goal.
Goal timing: The first month the modeled balance equals or exceeds the future-dollar goal. Arriving earlier does not make the goal inflation-adjusted.

Read the rate-range chart and several scenarios alongside the headline answer. A small change to a return or fee can compound into a large difference over a long horizon.

Worked example

A $1 million future-dollar goal

Hypothetical example: start with $100,000, contribute $1,500 at the end of each month, assume an 8% annual return compounded annually, invest for 20 years, and use no contribution increase, fee, or extra cash flow. The goal is $1,000,000. A 3% inflation assumption is used only to restate purchasing power; it does not change any nominal mode answer.

Mode	Calculator answer	How to read it
Final balance	About $1,319,594	The $100,000 start plus $360,000 of monthly deposits produces about $859,594 of modeled growth. At 3% inflation, the final balance has about $730,627 of today's purchasing power.
Starting investment	About $31,432	With the other assumptions unchanged, that starting sum is enough to finish at the $1 million goal.
Monthly contribution	$939	The precise modeled requirement is about $938.32; the interface rounds up to a whole-dollar plan that reaches the goal.
Return percentage	About 6.0% a year	This is the return the plan would need, not a forecast or a low-risk promise.
Time to goal	17 years, 1 month	At 8%, the modeled balance first crosses $1 million in month 205.

Each row solves a separate question. Do not combine the solved $31,432 start, $939 contribution, 6.0% return, and 17-year time into a new plan; each answer assumes the original values in the other fields.

Charts and tables, step by step

Every screenshot below uses the worked example in Final balance mode, with the $1 million goal enabled. The financial inputs stay the same throughout. Annual projection uses five-year display groups, and the last illustration duplicates the example to reveal Scenario comparison.

These are static screenshots of the calculator in its light theme. Hover over a numbered marker, focus it with the keyboard, or tap it to see the same explanation printed below the image. These notes focus on the calculation and controls that need interpretation; use the live calculator to open foldouts, change chart styles, inspect data, or export results. Hover, keyboard focus, and touch inspection reveal details on chart marks. K means thousands and M means millions.

Investment timeline

Follow when money enters the plan and when the goal is reached. This is a schedule across the full 20 years, rather than a chart of the total account balance.

Annual ending balance

Read how the ending balance builds from money you supplied and investment growth. The final column reconciles to the worked example: $100,000 + $360,000 + $859,594 = $1,319,594.

Stacked annual balances split into starting investment, contributions, and growth, with a $1 million goal line and goal-reaching years highlighted. — **Starting money.** The gray base remains $100,000 throughout this example.

**Contributions.** The blue segment accumulates the monthly deposits, reaching $360,000 by year 20.

**Growth.** The orange segment is cumulative investment growth, reaching about $859,594. It is separate from the money contributed.

**Goal and highlights.** The dashed line is the $1 million goal. Shaded columns show year-end balances that have reached it, starting in year 18. The timeline gives the earlier, exact month of crossing within that year.

Annual investment growth

This chart isolates growth earned during each year. It helps distinguish a year’s earnings from the cumulative growth segment in Annual ending balance.

Annual growth columns increasing from about $8,651 in year 1 to $97,017 in year 20. — **Annual growth columns.** Each column shows investment gain or loss during that year, excluding new deposits. Growth rises from about $8,651 in year 1 to $97,017 in year 20 under the steady 8% assumption. Both the growing balance and continuing deposits contribute to this pattern.

Return sensitivity

Compare what the same saving plan would finish with at different steady returns. This is a what-if comparison, not a probability distribution or a forecast.

Ending balances for returns from 5.5% to 10.5%, with the entered 8% return highlighted and step controls in the heading. — **Your 8% assumption.** The shaded column and bold 8% label identify the return entered in the form. Its ending balance is about $1,319,594.

**Legend and alternatives.** Orange includes the entered return and less favorable outcomes; blue identifies more favorable outcomes. Only the return varies across this chart.

**Balance scale and return axis.** The vertical axis is the final balance after 20 years. The horizontal axis is the assumed annual return, rather than elapsed years.

**Steps.** 10 means ten alternative returns on each side of 8%, plus the entered rate itself: 21 columns in total. The control allows 1–20 steps each side.

**Step size.** 0.25% means a gap of 0.25 percentage points between returns. With ten steps each side, this example runs from 5.5% to 10.5%. The allowed gap is 0.1–2 percentage points.

Required monthly contribution

Despite the short section heading, the plotted amount is the extra monthly contribution above the $1,500 already in the plan. The chart appears when a goal is enabled.

Extra monthly contributions needed to reach $1 million by earlier years, falling to zero at year 18. — **Extra contribution.** The legend is the key distinction: add the plotted amount to the existing $1,500 monthly contribution. Do not replace $1,500 with the plotted amount.

**Earlier deadlines.** Shorter deadlines need much more extra saving. Every column reruns the contribution solver with the same starting investment, return, timing, and $1 million goal.

**Zero extra at year 18.** The current plan already reaches the goal during year 18, so reaching it by that year-end needs no additional monthly saving. Year 17 still needs $2 extra per month.

**Goal years and tooltips.** The axis is the deadline year. The live tooltip reports both extra and total monthly contributions, so you can see the amount to add and the resulting monthly plan.

Annual projection

Use the table to reconcile the charts with exact displayed dollars. For this screenshot, Group is set to 5: all 20 years fit into four rows without changing the financial inputs.

Inflation-adjusted balance

Compare the projected account dollars with what those dollars could buy in today’s money. Inflation changes this purchasing-power view, while leaving the nominal growth projection unchanged.

Paired nominal and inflation-adjusted annual balances, ending at $1,319,594 and about $730,627 respectively. — **Nominal balance.** The year-20 orange column is about $1,319,594: the same final balance shown elsewhere.

**Today’s purchasing power.** The year-20 gray column is about $730,627 in today’s money. The $1 million goal remains a future-dollar goal; inflation does not automatically increase it. The gap between the two balances represents purchasing power, not a separate fee deducted from the account.

Cash-flow schedule

This table lists extra scheduled deposits and withdrawals. The worked example has none, so the empty state and both $0 totals are correct. The regular $1,500 monthly contribution still appears in the projection and timeline.

Cumulative fee impact

Compare the same plan with different annual balance fees. The example’s input remains 0%; the chart adds 0.5% and 1% alternatives automatically to illustrate how fees affect compounding.

Three after-fee balance lines for 0%, 0.5%, and 1% fees, with a $183,946 final-balance reduction for the 1% alternative. — **Fee legend.** “No fee · your fee” is the example’s zero-fee plan. The other series apply 0.50% and 1.00% fees while keeping deposits and the assumed return the same.

**Three balance paths.** The lines separate as fees reduce both the balance and its later growth. Hover, focus, or tap a year in the calculator to compare each after-fee balance and cumulative fee drag.

**Fee-impact callout.** The 1% alternative reduces the final balance by about $183,946 versus no fee. This difference includes forgone growth, not just fees directly charged.

Scenario comparison

This table appears when more than one scenario is present. For this illustration, use Add another scenario to duplicate the worked example and name the two copies “Worked example” and “Worked example copy.” No financial input changes, so every result matches.

Two identical worked-example scenarios with matching ending balances, contributions, growth, purchasing power, and goal timing. — **Money supplied and growth.** Money you put in includes the $100,000 start and $360,000 of deposits. Growth on top is the separate $859,594 gain.

**Today’s dollars.** Both plans have about $730,627 of today’s purchasing power because they use the same 3% inflation assumption.

**Goal timing.** Both first reach $1 million after 17 years, 1 month. Changing a scenario later lets you compare these outcomes side by side.

Assumptions and limitations

The main projection uses a steady return. Actual investments rise and fall, and losses early or late can produce outcomes unlike a smooth average.
Returns, inflation, fees, and tax are assumptions rather than recommendations. Test several plausible combinations, including lower returns and higher costs.
The fee field models a percentage charged against the balance. It does not automatically include trading costs, advice charges, sales loads, or taxes; the calculator has no separate tax field. Investor.gov's fee guide explains why the full cost matters over long periods.
A nominal goal can lose purchasing power. If the goal represents today's lifestyle or price, estimate its future-dollar amount or compare the result shown in today's money.
An account is never allowed below zero. If a fixed withdrawal exceeds the available balance, the projection caps the payment and records the rest as unmet. Backward solvers search the same settled state machine and require both no material withdrawal shortfall and the requested ending goal.
The calculator does not model a particular security, asset allocation, investment risk, account rule, or guarantee. Rounded display values can differ slightly from the internal calculation.

Sources and further reading

Sources reviewed August 2026. These sources explain the financial concepts; they do not endorse this calculator or its assumptions.

Investor.gov: Compound Interest Calculator — definitions for an initial investment, monthly contributions, time, estimated interest rate, and compounding frequency.
Investor.gov: Understanding Fees — why even small ongoing investment costs can have a large long-term effect.
U.S. Bureau of Labor Statistics: Purchasing power and constant dollars — how inflation and constant-dollar measures relate future money to purchasing power.

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