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Investing maths,
in plain English.
31 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 31 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 depositHow much difference does dividend reinvestment make?
Take the dividend as cash or let it buy more of the same thing. Same yield, same growth — see the gap compounding the dividend actually produces.
Dividend reinvestmentHow much do I need to buy and sell to rebalance?
Enter what each holding is worth and the split you are aiming for. See the exact trades, and how much new money would do the job without selling anything.
RebalancingHow much interest will my savings earn?
Enter a balance, monthly deposits and the rate. See the interest credited, and whether the balance actually keeps up with prices.
Savings interestWhat is my net worth?
Add up what you own and what you owe. See the total, where it comes from, and how much of it is the house.
Net worthHow long until refinancing pays for itself?
Closing costs against the new payment, month by month. See when you are ahead counting the balance still owed — not just the cheaper payment.
Refinance break-evenWhen can I retire early?
Your savings rate, turned into years to financial independence. It counts twice: what you save builds the pot, and what you spend sets its size.
FIRE dateWhat is my savings rate?
The share of your pay you actually save — pension and employer money included — and what that rate builds over a working life.
Savings rateIs it better to rent or buy a home?
The same budget spent two ways: buying, or renting and investing the difference. See who is ahead when the home is sold, and how much that hangs on the guesses.
Rent vs buyA 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.
- Is a 3% raise good? Do the arithmetic"Good" is not a feeling. It is a comparison with inflation and tax, and it takes about a minute.
- How much more should a contractor make?There is no single percentage. There is a sum, and the biggest part of it is days you cannot bill.
- T-bills vs high-yield savings, after taxComparing the two headline rates is the wrong sum for anyone who pays state income tax. Here is the right one.
- Why is my credit card minimum payment going up?A minimum normally shrinks as you pay the card down. When it grows instead, something specific changed.
- Why is most of my mortgage payment interest?Nobody front-loaded anything. Interest is charged on what you still owe, and at the start you owe almost all of it.
- Marginal tax rate vs effective tax rateOne is the rate on your next dollar, the other is the average on all of them. Mixing them up is where the bracket myth comes from.
- Should I overpay my mortgage or invest?The arithmetic has exactly one break-even point, and it is printed on your mortgage statement. Everything else is a question about risk.
- Lump sum vs dollar-cost averaging: the real gapSpreading a windfall in has a price. It can be measured, it is usually smaller than the argument about it, and it buys something real.
- Is the 4% rule still valid?It was never a forecast. It was the worst case in one country’s history, under assumptions most people never read.
- Debt snowball vs avalanche: which is better?On interest alone the avalanche almost always wins. The useful question is by how much, and that depends on your debts.
- APR vs APY: what each rate actually countsOne is a yearly rate before compounding, the other after it. Which one you are shown depends on whether you are borrowing or saving.
- What CAGR actually measuresOne steady rate that links a start value to an end value. It is honest about the destination and silent about everything in between.
- Nominal vs real return: which one to useOne counts dollars, the other counts what dollars buy. Both are correct. The mistakes come from mixing them in the same sum.
- Why is the first 100k the hardest?The saying is true for most savers, and the arithmetic says exactly why. It also says who it is not true for.
- How much should I save?Any one-size answer is a rule of thumb built around somebody else. Yours is a sum, worked backwards from the goal.