Savings goal — the shortfall is not the answer
A projection tells you where you land. It does not tell you what to move.
Knowing you are short is the easy part. The monthly number that closes it is the answer. Set your goal, then
see why the usual comparison fails.
$462,400
$500 a month for twenty years at 7% real, on $50,000 invested.
$37,600
Close enough to feel like rounding, far enough to miss by.
Does your plan structurally produce your goal?
Discipline is the fuel; structure is the vehicle. This solves your plan backward — the contribution your goal actually requires, against the one you are making today.
| Variable | The goal requires | Your current plan | The gap |
|---|
The three levers
Each lever closes the whole gap on its own, holding the other two where you set them. That is the point — you are choosing which one to move, not hoping all three drift your way.
Nothing here leaves your browser. The image is built and saved on this device; "Copy data" copies your full figures to your own clipboard.
Educational content only — not financial advice. Figures assume a constant real return and a contribution made at the end of each month. Real markets do not deliver a constant return; this models the structure of a plan, not a forecast of one.
A projection tells you where you land. It does not tell you what to move.
Every retirement calculator runs the same way round: put in what you are doing, and it prints where you end up. That is the wrong direction. You already know what you are doing. What you need is the size of the shortfall and the specific thing that closes it.
$462,400
Twenty years of $500 a month at 7% after inflation, on top of $50,000 already invested. A perfectly respectable plan, run honestly.
$37,600
Close enough to feel like a rounding error, far enough to miss by. The projection alone never tells you this, because it never asked what you were aiming at.
Once you have the gap, there are only ever three things you can move, and this tool solves each one backwards so that every lever closes the whole gap on its own, holding the other two exactly where you set them. On the plan above: contribute $572.18 a month instead of $500. Or keep contributing $500 and run for eleven and a half more months. Or earn 7.50% real instead of 7.00%.
That is the useful output, and it is also where the honesty lives, because those three are nothing like equally difficult. Seventy-two dollars a month is a decision you can make this afternoon. Eleven more months is uncomfortable but yours to choose. Half a percentage point of extra real return, sustained for two decades, is not a decision at all — it is a hope, and the one lever a calculator should never encourage you to lean on.
Presented as three tidy options they look interchangeable. They are not. The point of seeing all three is choosing which one you are actually going to move, rather than hoping all of them drift your way — which is the default plan of nearly everyone who has never run the numbers backwards.
Nothing here is hidden. Check every line.
One example plan — a $500,000 goal, twenty years, 7% after inflation, $500 a month, $50,000 already invested — taken apart so you can audit the method before you trust it on your own figures.
| Where the money comes from | You put in | It becomes |
|---|---|---|
| The $50,000 already invested | $50,000.00 | $201,936.94 |
| $500 a month for 240 months | $120,000.00 | $260,463.33 |
| What the plan produces | $170,000.00 | $462,400.27 |
| Against a $500,000 goal | — | −$37,599.73 |
| Three levers, each closing the whole gap alone | Now | Required | The move |
|---|---|---|---|
| Contribute more | $500.00 | $572.18 | +$72.18 a month |
| Run for longer | 20.00 yrs | 20.95 yrs | +11.4 months |
| Earn more | 7.00% | 7.50% | +0.50 points |
The three levers are priced the same and cost wildly different things
Look at the last column and it reads like a menu of equivalent options. It is not. Seventy-two dollars a month is a decision — you can make it before lunch and it is entirely within your control. Eleven more months is also a decision, less pleasant, still yours. Half a percentage point of extra real return, held for twenty years, is neither. Nobody can decide to earn it, and the usual routes to reaching for it — more risk, more trading, more concentration — carry a real chance of landing you well below 7% instead.
That is why the return lever exists on the screen and should almost never be the one you pull. The tool will happily solve it, and it will also refuse to flatter you: when no realistic figure closes the gap it stops printing a percentage and says so, because a plan that needs an implausible return is not a plan with an ambitious assumption, it is a plan that has to be fixed with income or with time.
Two things the model does not do, both worth knowing. The return is real — after inflation — so the target is in today’s money and you are not being shown a large number that quietly buys less. And the monthly contribution is held constant in real terms: it neither rises with your income nor decays with prices. If your contribution grows as you earn more, you will beat this. If it stays nominally flat for twenty years, you will not, because it shrinks against inflation every year you leave it alone.
It solves the plan backwards.
Five inputs, no account, no email. And unlike most of the tools on this site, this one has no server side at all — nothing you type here ever leaves your browser.
Name the target
The capital the goal actually needs, in today’s money. If you are thinking in income rather than capital, work backwards: $3,000,000 supports roughly $10,000 a month at a 4% withdrawal rate.
Name the horizon and the return
How long the plan has to run — up to sixty years — and a return after inflation. Use the same figure you would use anywhere else. The gap should come from structure, not from a more optimistic assumption.
State what you are actually doing
The monthly amount you genuinely contribute now, not what you intend to, plus whatever is already invested. That existing capital compounds for the full horizon, which is why it usually does more work than people expect.
Read the three levers
The gap, then each of contribution, time and return solved to close all of it alone, with the other two held exactly where you set them. You are choosing which one to move, not hoping all three drift your way.
Nothing leaves your browser, and two assumptions you should hold onto
This tool has no server side. Not a reduced one — none. There is no account, no email gate, no sign-up, and no network request of any kind: the arithmetic runs in the page on your own device, and the figures you type are never transmitted anywhere, because there is nowhere for them to be transmitted to. The exported image is built and saved on your machine, and putting your own dollar amounts on it is an opt-in checkbox rather than the default. That matters more here than on most calculators, because the numbers this one asks for are the whole shape of your finances.
The first assumption is a constant real return, and the tool says so in its own footer: real markets do not deliver a constant return, and this models the structure of a plan rather than a forecast of one. Two portfolios that both average 7% can land in very different places depending on the order the good and bad years arrive in. What a constant rate is genuinely good for is the question being asked here — how big is the gap, and what closes it — because that answer barely moves under a different path.
The second is that your contribution is held flat in real terms for the whole horizon. It does not rise with your income and it is not eroded by inflation. That cuts both ways and it is worth knowing which side you are on: if you increase what you put in as you earn more, you will beat this projection. If you set up a standing order years ago and have never touched the figure, you are doing worse than the model says, because a nominally fixed contribution buys a little less every single year.
Most complaints about this tool are correct.
A single smooth rate pointed at twenty years of a real life. That is a strong simplification, and here are the four arguments against the output that actually land.
“Markets do not return a constant 7% a year.”
Correct — and the tool says so itself
They do not, and nothing here pretends otherwise. Returns arrive in an order, and the order matters enormously: two portfolios that both average 7% can finish in very different places depending on when the bad years land. This models the structure of a plan, not a forecast of one.
What saves the answer is the narrowness of the question. A smooth rate is a poor way to predict where you end up and a perfectly good way to ask how far short you currently are and what closes it. The gap and the three levers barely move under a different path; the endpoint moves a great deal. Use it for the first question only.
“Then I will just assume a higher return.”
This is the one way to misuse the tool
The three levers sit side by side and look interchangeable. Two of them are decisions and one is a hope. You can decide to contribute more. You can decide to run longer. Nobody can decide to earn half a point more real return for twenty years, and reaching for it usually means more risk, more concentration or more trading, each of which can land you well below where you started.
So closing a gap by raising the return field has closed nothing. The tool will solve it because refusing to would be paternalistic, and it will also stop printing a number entirely when no plausible return works, and tell you plainly that this one has to be solved with income or time.
“My contribution will not stay flat for twenty years.”
Correct — and it cuts both ways
The model holds your monthly amount constant in real terms for the whole horizon. It neither grows with your income nor decays with prices, and almost nobody’s actually behaves that way.
Which direction you are wrong in is the useful part. If you raise your contribution as you earn more, you will beat this projection, possibly by a wide margin. If you set up a standing order years ago and have never revisited the figure, you are doing worse than this says — a nominally fixed contribution buys a little less every year, and the plan quietly shrinks while looking untouched.
“How would I even know the right target?”
Fair — and the tool has no opinion on it
It takes your target as given and measures the distance to it. It does not know what you will spend, when you will stop, what else will pay you, or whether the number you typed bears any relation to the life you want. A wrong target produces a confident answer about the wrong question.
The one thing it can do is make the target legible. If you are thinking in income rather than capital, convert it before you start — $3,000,000 supports roughly $10,000 a month at a 4% withdrawal — and then at least the number you are aiming at means something specific to you.
Built for people who intend to move something.
One question, answered properly, once. If what you actually need is something else, the honest answer is that this will not give it to you.
It fits if
- You have a number you are aiming at and a contribution you are actually making, and have never put the two side by side to see whether one produces the other.
- You suspect you are slightly short and want the shortfall quantified rather than felt — along with the specific increase that closes it.
- You are choosing between saving more and working longer, and want both priced against the same goal instead of argued about.
- You want the arithmetic to happen on your own machine. Nothing you type here is transmitted anywhere, because there is no server side to transmit it to.
It does not fit if
- There is no slack anywhere — nothing to add, no time to add, and nothing to cut. All three levers need something to move, and a plan with nothing spare is an income problem, not a planning one. No calculator fixes that.
- You intend to close the gap by raising the return field until it goes green. That solves the screen and nothing else, and the answer you take away will be worse than no answer.
- You want a forecast of what you will actually have. It assumes a constant real return, which real markets do not deliver; it sizes a gap, it does not predict an outcome.
- You do not yet know what you are aiming at. The tool takes your target as given and has no view on whether it is the right one — a wrong target produces a confident answer to the wrong question.
The contribution your goal actually requires.
Answered against what the tool actually does, not against what would be convenient to claim.
How much should I save each month to reach my goal?
It falls out of four things: the target, the years you have, the real return you assume, and whatever is already invested. Worked on one example — a $500,000 goal, twenty years, 7% after inflation, $50,000 already invested — the required contribution is $572.18 a month.
The formula is not a secret. Grow the existing capital, work out what the remainder needs to be, and divide by what a monthly stream compounds to: pmt = (target − start × growth) × i / (growth − 1), where i is the monthly rate. Enter your own four numbers and the tool does exactly that.
How do I work out the gap in my savings plan?
Project what you are currently doing, then subtract it from what you need. On the same example plan — contributing $500 a month rather than the required $572.18 — twenty years produces $462,400.27 against a $500,000 goal. The gap is $37,599.73.
Worth seeing where that total comes from: the $50,000 already invested becomes $201,936.94, and $120,000 of actual contributions becomes $260,463.33. Existing capital does more work than most people credit, because it compounds for the entire horizon rather than arriving in instalments.
What can I change to close the gap?
Only three things, and the tool solves each one so that it closes the whole gap on its own, holding the other two fixed. On the example: contribute $72.18 more a month, or run the plan for about eleven and a half months longer, or earn 7.50% real instead of 7.00%.
They are not equivalent, and this is the part worth carrying away. Two of them are decisions and one is a hope. You can choose to add seventy-two dollars a month or to work another year. Nobody can choose to earn an extra half a point of real return for two decades — and reaching for it usually means more risk, which can just as easily widen the gap.
What if no return is high enough to close the gap?
Then the tool stops printing a percentage and tells you so. Beyond a certain point the solver reports that no return closes this gap rather than producing an absurd figure to fill the box.
That is deliberate, and it is the most useful thing the tool says. A plan requiring an implausible return is not a plan with an ambitious assumption; it is a plan that has to be fixed with income or with time. Printing a number there would let you believe the arithmetic had solved something when it had only relabelled the problem.
Are the figures adjusted for inflation?
Yes. The return you enter is a real return — after inflation — so the target and every projected figure are in today’s money. You are not being shown a large future number that quietly buys less than it appears to.
One consequence to hold onto: your contribution is held constant in real terms too. It neither rises with your income nor decays with prices. If you increase what you put in as you earn more, you will beat this. If you set a standing order years ago and never revisited it, you are doing worse than this projection says, because a nominally fixed amount buys less every year.
Is my data saved or sent anywhere?
No, and on this tool the answer is stronger than on most. There is no server side at all. Not a limited one — none. The arithmetic runs entirely in the page on your own device, and there is no account, no email gate, no sign-up and no network request of any kind: the figures you type cannot be transmitted anywhere because there is nowhere for them to go.
The exported image is built and saved on your own machine, and putting your dollar amounts on it is an opt-in checkbox that starts unticked. The only thing this page stores in your browser is whether you chose dark mode.