Reverse Investment Calculator: Free Goal Planner
Most investment calculators run forward: you enter what you have and they tell you what you get. This one runs backwards. Set the future amount you want and it solves for the lump sum to invest today, the periodic payment needed along the way, or the annual return your plan requires. A year-by-year schedule shows how the balance builds, and an optional inflation toggle restates the goal in today’s dollars so you are planning for purchasing power, not a nominal number.
Projection only, not investment advice. Assumes a constant annual return compounded at the contribution frequency, with contributions at the end of each period. Real returns vary.
Quick Answer
Goal: $1,000,000 in 30 years at 8% a year, contributing monthly and starting with $10,000. You need to invest $597.60 a month: $10,000 + $597.60 × 360 = $225,136.94 out of pocket, and compound growth covers the remaining $774,863. With 3% inflation, that $1M buys what $411,987 buys today. The calculator above opens with this exact plan, so click Calculate to reproduce it, then switch the solver to check the lump-sum and required-rate angles.
Key takeaways
- One input set solves four unknowns: the lump sum today, the periodic payment, the required return, or the time needed. Most rival tools solve only one of them.
- Contributions are modelled at the end of each period, so the first payment earns interest for one period less than the lump sum does. That convention is stated on the tool and in the schedule.
- Every solver round-trips: feed its answer back into the forward equation and you land on the goal within a cent. The page tells you exactly how to check that.
- Inflation is the silent second variable. A $1M goal in 30 years at 3% inflation is $411,987 of today's purchasing power, so plan for the real figure, not the nominal one.
- Quick Answer
- How to use the reverse investment calculator
- Solving the time-value equation backwards
- Worked example: the million-dollar plan, four ways
- Why the inflation toggle matters
- Reading the year-by-year schedule
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the reverse investment calculator
Pick which unknown you want to solve for, fill in everything else, and click Calculate. The results stay hidden until you calculate, and Reset restores the worked-example plan so you can start over in one click.
- Choose "Solve for". Lump sum (PV) answers "what do I invest today"; Periodic payment (PMT) answers "what do I add every month"; Required rate of return answers "what annual return does this plan need"; Time needed answers "how long until I reach the goal". The field you are solving for hides itself.
- Enter the target future amount. This is the nominal goal at the end of the plan; the inflation field restates it in today's dollars beside it.
- Fill in the knowns. Starting lump sum, periodic contribution, annual return, years (except when solving for time), and the contribution frequency. Match the frequency to the investment you are modelling: savings accounts and most bonds compound monthly or quarterly, CDs often compound daily or monthly, and simple projections use annual compounding.
- Read the answer, the formula line and the schedule. The headline gives the solved unknown; the formula line shows the exact arithmetic; the year-by-year table shows how the balance builds from opening to closing each year.
Every input is validated before any math runs: blank fields, a non-positive target, negative amounts, rates above 500%, years outside 1–100 and negative inflation each get a specific plain-English error. If your plan is already overfunded, the tool says so plainly ("no lump sum is needed") instead of returning a negative number.
Solving the time-value equation backwards
The forward math grows what you have: FV = PV × (1 + r)^n + PMT × (((1 + r)^n − 1) ÷ r), where r is the per-period rate and n the number of periods. Solving for the lump sum or the payment is algebra: isolate the unknown and divide. Solving for the rate has no closed form, so the tool uses bisection, repeatedly halving a rate interval until the forward calculation lands within a cent of the target.
PV = (FV − FV of contributions) ÷ (1+r)^n | PMT = (FV − PV(1+r)^n) × r ÷ ((1+r)^n − 1)
Rate: found by bisection; the forward check round-trips to the goal within a cent.
Time: found by bisection on years; the forward check round-trips to the goal within a cent, and the schedule rounds up to whole years.
Contributions are modelled at the end of each period (the ordinary-annuity convention used by the SEC's own compound interest illustrations): each payment earns interest from the period after it is made. That is why the year-by-year schedule adds the payment after the period's growth, and why the closed-form and the schedule always agree with each other.
Worked example: the million-dollar plan, four ways
Goal $1,000,000 in 30 years at 8% a year, monthly contributions, starting from $10,000. All four solvers run on the same inputs, so you can flip the "Solve for" dropdown and check each answer against the others.
| Solver | Answer | What it means |
|---|---|---|
| Lump sum (PV) | $23,301.63 | Invest $23,301.63 today and add $500 a month; the $500 stream grows to $745,179.72 and the lump sum covers the rest. |
| Payment (PMT) | $597.60 / month | $10,000 + $597.60 × 360 = $225,136.94 out of pocket; growth covers the remaining $774,863. |
| Rate | 8.72% | With $10,000 down and $500 a month, you need 8.72% a year; the forward check lands on $999,999.99, within a cent of the goal. |
| Time needed | 31.8 years | $10,000 down and $500 a month at 8% reaches $1,000,000 in about 31.8 years (382 months); the schedule rounds up to 32 years. |
Verify the payment solver yourself: solve for the payment, note $597.60, then switch to the rate solver and enter $597.60 as the contribution, or grow $23,301.63 from the lump-sum solver at 8% with $500 a month. All four answers describe the same plan. Check the time solver the same way: 31.8 years at 8% with $10,000 down and $500 a month forward-checks to $1,000,000. The reverse present value calculator handles the simpler no-contributions case if you only need a lump-sum reversal, and the investment fund calculator projects an existing fund forward for comparison.
Why the inflation toggle matters
A $1M goal in 30 years at 3% inflation buys what $411,987 buys today: 1,000,000 ÷ 1.03^30. Naming the goal in today's dollars keeps the target honest, because it is the purchasing power that matters, not the nominal figure. Enter your inflation assumption and the tool reports both numbers side by side, in the results and in the formula line.
The BLS inflation calculator shows how much prices have actually moved over any past period, which is the honest starting point for the assumption you type in here. One caution: the toggle restates the GOAL in today's dollars; it does not shrink the contributions or the schedule, which stay nominal. That keeps the math auditable but means the "today's dollars" line is a planning read, not a second plan.
Reading the year-by-year schedule
Every result comes with a full schedule: opening balance, contributions, growth and closing for each year, so you can watch the crossover point where growth starts doing more work than your payments.
In the worked plan, year 30 closes at $1,000,000 exactly, with $76,386 of that year's growth coming from compounding on the earlier balance. If the schedule's final line does not land on your goal, something in the inputs changed between solvers, because the schedule is built from the solved values themselves. For retirement-specific planning with tax-advantaged accounts, the Roth IRA investment calculator models that account's rules, and the ETF investment calculator projects a fund-based portfolio forward.
What competing calculators miss
Plenty of tools solve for the monthly payment needed to reach a goal, and a few also offer an inflation restatement. But most solve only one unknown: you get the payment, not the lump sum or the required return, and the answers cannot be cross-checked against each other. Schedules are the other common gap; many tools give one number and no audit trail.
- Four solvers, one input set: flip the dropdown to check the lump sum against the payment against the rate, all describing the same plan.
- Round-trip disclosure: the rate solver states its method (bisection) and the tolerance (within a cent), and the formula line shows the forward check, so the answer is verifiable by hand.
- Honest edge behaviour: an overfunded plan gets "no lump sum is needed" instead of a negative dollar figure, and a 0% return is handled exactly rather than dividing by zero.
- The full schedule: every year accounted for, opening through closing, so the crossover where growth overtakes contributions is visible, not hidden.
Frequently asked questions
Choose "Lump sum to invest today", enter your goal, the periodic contribution you will keep making, the annual return, years and frequency. For a $1,000,000 goal in 30 years at 8% with $500 monthly contributions, the lump sum is $23,301.63.
Choose "Periodic payment needed" and enter the goal, your starting lump sum, the annual return, years and frequency. A $1,000,000 goal in 30 years at 8% from $10,000 needs $597.60 a month, or $225,136.94 out of pocket in total.
Choose "Required rate of return" and enter the goal, starting lump sum, periodic contribution, years and frequency. With $10,000 down and $500 a month toward $1,000,000 in 30 years, the plan needs 8.72% a year, and the forward check lands on $999,999.99.
The rate sits inside an exponent, so there is no closed form. This calculator uses bisection: it repeatedly halves a rate interval and runs the forward equation until the result lands within a cent of the goal. The formula line shows that forward check, so the answer is verifiable.
At the end of each period. That is the ordinary-annuity convention: each payment earns interest from the following period onward. The tool states this under the results, and the year-by-year schedule adds each payment after the period's growth, so the two always agree.
It restates your goal in today's dollars alongside the nominal figure. A $1,000,000 goal in 30 years at 3% inflation equals $411,987 of today's purchasing power. The schedule and contributions stay nominal; only the goal gets the real-dollars reading.
Cross-check them against each other. Grow the lump-sum answer ($23,301.63) at 8% with $500 monthly contributions for 30 years and you land on the $1,000,000 goal; the rate solver's forward check is printed in the formula line to the cent. If your plan is overfunded, the tool says so instead of returning a negative number.
No. It is an educational planning tool that assumes a constant annual return, which real markets do not deliver. Actual returns vary year to year, and taxes and fees are not modelled. Treat every figure as a planning estimate, not a forecast.
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References
- U.S. Bureau of Labor Statistics. CPI Inflation Calculator. Accessed October 23, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Compound Interest Calculator. Accessed October 23, 2026.
- Consumer Financial Protection Bureau. Ask CFPB: What is compound interest?. Accessed October 23, 2026.
- FINRA. Learn to Invest: Key Investing Concepts. Accessed October 23, 2026.
- U.S. Department of the Treasury, TreasuryDirect. Savings Bonds. Accessed October 23, 2026.
- Internal Revenue Service. Retirement Plans. Accessed October 23, 2026.
- Consumer Financial Protection Bureau. Managing Your Money, Part 2: Compound Interest Worked Example. Accessed October 23, 2026.
- U.S. Department of Labor. Top 10 Ways to Prepare for Retirement. Accessed October 23, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Introduction to Investing. Accessed October 23, 2026.
- Federal Deposit Insurance Corporation. FDIC Money Smart Financial Education. Accessed October 23, 2026.