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Investing maths,
in plain English.
23 calculators. No sign-up, no email wall, nothing to install. Every answer comes with a plain-English sentence and an honest range instead of one confident-looking number.
What could your money grow to?
Open the full pageWhat you already have, if anything.
A starting point, not a forecast. Change it and watch how much the answer moves.
More options(5)
Fund charge plus platform charge. Comes straight off the return.
Used only to show what the pot is worth in today's money.
Increases the monthly amount once a year, the way a pay rise would.
After 25 years, if returns average 7%
$201,188
Putting in $250 a month on top of $1,000 you already have, you would pay in $76,000 in total. The other $125,188 — 62% of the final pot — is growth you never contributed.
- You pay in
- $76,000
- Growth on top
- $125,188
- Growth as a share of the pot
- 62%
If returns average…
Nobody knows which of these happens
| Assumption | Final pot | Of which growth |
|---|---|---|
| 4% a year — cautious | $129,878 | $53,878 |
| 7% a year — middle | $201,188 | $125,188 |
| 10% a year — optimistic | $319,166 | $243,166 |
Markets do not return the same amount every year. The band shows the same plan under three different assumptions, so you can see how much the answer depends on a number nobody knows.
All 23 calculators
Each one runs in your browser as you type. Nothing is sent anywhere, and the address bar carries your numbers so you can bookmark a scenario or send it to someone.
How much of my salary do I actually keep?
Gross to net, with the full breakdown — plus the figure payslips never print: what the next unit of salary is really worth.
Take-home payWhat day rate do I need to go freelance?
Your salary was never the whole package. See what the job is really worth, and the day rate that replaces it.
Employee vs freelanceWhat day rate do I need to charge?
Start from the income you want. See the rate that produces it once tax set aside and unbillable days are counted properly.
Freelance rateDid my pay rise keep up with inflation?
Raise minus inflation is the wrong sum. See the real change, what tax takes of it, and what a run of these years adds up to.
Raise vs inflationWhat could my money grow to?
Put in what you have and what you add each month. See what it becomes, and how much of that you never paid in.
Investment growthHow much a month do I need to save?
Name a target and a deadline. Get the monthly figure that reaches it under each return assumption.
Monthly amountHow much do investment fees really cost?
A 1% charge sounds small. Over thirty years it is not. See the figure in money rather than percent.
The fee checkHow much do I need to retire?
Start from what you spend in a year, not from a round number someone else picked.
Your numberHow long will my savings last?
Spend from a pot while it is still invested, with the withdrawal rising to keep pace with prices.
How long it lastsWhat will my money be worth in the future?
Both directions: what today’s amount will cost in future, and what a future amount is worth now.
InflationCan I stop saving and still retire on time?
The amount that, left completely alone, grows into your retirement pot by itself. Everything after that is optional.
Coast FIREIs it better to invest a lump sum or spread it out?
Put the same money in on day one or drip it in over months. See the gap the arithmetic actually produces.
Lump sum or spreadWhat are the monthly repayments on a loan?
The monthly payment on any loan, plus the number nobody leads with: how much of what you repay is interest.
Loan repaymentsHow long until my first 100k?
Every milestone from your first 10k to your first million, and how the wait between them keeps shrinking.
MilestonesHow long will it take to pay off my debt?
Name the balance, the rate and what you pay each month. See how long it takes, what it costs in interest, and what paying more actually saves.
Debt payoffHow long to pay off a credit card paying the minimum?
The minimum falls as the balance falls, which is why it takes decades. See the years, the interest, and the fix that costs nothing this month.
Minimum paymentIs it worth overpaying my mortgage?
Add a fixed amount to the monthly payment and see the years and interest it saves — priced against a guaranteed return, not a guess.
Mortgage overpaymentWhat is the CAGR of an investment?
Enter a start value, an end value and the years between them. Get the single steady rate that actually explains the gap — not the average of the yearly returns, which reads higher.
CAGRWhat is the real rate of return after inflation?
Nominal return minus inflation is the wrong sum. See the exact figure, and how far off the shortcut version really is.
Real returnHow much do Treasury bills pay right now?
Opens on today’s published yield curve. Includes the state tax exemption, which is what makes the comparison against savings interesting.
Treasury billsHow much should I have in an emergency fund?
Say what you spend each month and what you already have saved. See how many months that covers, and how long the rest takes at your saving rate.
Emergency fundDebt snowball vs avalanche: which pays off faster?
Enter every balance once. See both payoff orders run side by side, and the actual size of the gap between them.
Snowball vs avalancheHow long will it take to save for a house deposit?
The target is not what a deposit costs today — it is what it will cost when you actually get there, because house prices do not wait for you to save.
House depositA sentence, not just a number
Every result comes with a line explaining what it means — generated from the same figures, so it can never disagree with the chart above it.
A range, not a promise
Nobody knows what markets will return. Each tool prices your plan under three assumptions so you can see how much the answer depends on a guess.
No account, ever
No sign-up, no email wall, no analytics, no affiliate links to brokers. The site is paid for by ads, which buys no influence over a single number on it.
Read first, if you like
All guidesShort pieces explaining the ideas behind the tools. No opinions about what you should buy — this site does not have any.
- What compounding actually isThe one idea the whole site rests on, explained without the snowball metaphor.
- Returns are not a straight lineWhy every calculator on the internet — including this one — draws a curve that will not happen, and what to do about it.
- What an index fund isA plain description of the thing, with no opinion about whether you should own one.
- Fees, explained properlyExpense ratios, platform charges and the reason a percentage is the wrong unit to think in.
- A short glossaryTwenty-odd terms you will hit in your first month, defined in one line each.