Investor Financial Planning Hub

Simple Tools for Investors

Six calculators for everyday money questions, with the arithmetic written out in front of you. Start from the question, open the calculator, and change the figures to match your own.

Worked examples you can check by hand

Each figure below is the output of the calculation function the named tool calls, for the inputs printed with it. The compound calculator rounds to whole dollars on screen, so its own table reads $196,665 where this page prints $196,665.39. The loan calculator prints cents, so its three figures match exactly.

$300 a month at 7% for 20 years

Inputs: $10,000.00 starting balance, $300.00 added at the end of every month, 7% a year compounded monthly, 20 years.

Compound interest projection for a $10,000.00 starting balance with $300.00 added monthly at 7% over 20 years.
Measure	Year 10	Year 20
Money you put in	$46,000.00	$82,000.00
Interest earned	$26,022.06	$114,665.39
Balance	$72,022.06	$196,665.39

You deposit $82,000.00 in total and the account ends at $196,665.39, so the interest is 139.84% of everything you paid in.
In the second decade you add another $36,000.00 and the balance grows by $124,643.33.
Switch on the 2.5% inflation adjustment and the same $196,665.39 buys what $120,019.17 buys today.

Try it in the Compound Interest Calculator

One doubling, two holding periods

Inputs: a $10,000.00 balance that reached $20,000.00, measured once over 5 years and once over 20 years.

Annual rate for a $10,000.00 balance that doubled to $20,000.00, over 5 years and over 20 years.
Holding period	Total return	Annual rate	Growth
5 years	100.00%	14.87%	×2.000
20 years	100.00%	3.53%	×2.000

Both holdings returned everything they started with, twice over. Read as an annual rate, one is 14.87% and the other is 3.53%.
The CAGR Calculator reads a starting value, an ending value, and a duration, then returns the annual rate, the total return, and how many times the value grew.

Try it in the CAGR Calculator

What a $320,000.00 mortgage costs over 30 years

Inputs: $320,000.00 borrowed at 6.25% a year over a 30 year term.

Fixed rate loan totals for $320,000.00 borrowed at 6.25% over a 30 year term.
Line	Amount
Monthly payment	$1,970.30
Number of payments	360
Total paid	$709,306.21
Total interest	$389,306.21

Interest takes 54.9% of the $709,306.21 you hand over, on top of returning the $320,000.00 you borrowed.

Try it in the Loan & Mortgage Calculator

Which calculator answers which question

Rows are ordered by question rather than by tool. Find the line that sounds like your problem and open that calculator.

Which calculator answers which investor question, and what each one shows
Your question	Calculator	What it shows you
What will my savings be worth if I keep adding to them?	Compound Interest Calculator	A year-by-year table, a growth chart, and the interest earned so far.
Did my balance keep up with inflation?	Compound Interest Calculator	The same projection restated in today money, year by year.
What did an investment return per year?	CAGR Calculator	The annual rate, the total return, and how many times the value grew.
What does this mortgage or auto loan really cost?	Loan & Mortgage Calculator	The monthly payment, the number of payments, and the total interest.
What share of my portfolio sits in one asset?	Percentage Calculator	Find a share of a total, add or subtract a percentage, or solve for a retail margin, in seven currencies, with the formula each figure came from.
Is this sale a real discount, and what do I save?	Discount Calculator	Stacked codes, sales tax charged after the discount, and the amount saved.
Quick arithmetic while I read a statement	Simple Calculator	Keyboard entry and a history of your last 20 calculations.

How to use these calculators

1
Start from the number you do not have
Decide what you are trying to find: the future value of a savings plan, the annual return on a holding, or the total cost of a loan. The question picks the calculator, not the formula.
2
Enter the figures you actually have
Type the values the calculator asks for: a starting amount, a rate, a term, a holding period, or a recurring contribution. Each one labels what it asks for and names the figure it returns, and none of them asks for an account.
3
Compare the result against the number that decides it
Balance against the total you deposited, annual rate against a benchmark, total interest against the amount borrowed. That comparison is the part a spreadsheet makes you build yourself.

What happens to the numbers you type

Your inputs are read by JavaScript in your own browser. None of the six calculators makes a network request with what you typed.
The analytics tracker keeps an allowlist of keys per event and refuses any key that names user content, such as input, value, output, result, text, or token.
Cloudflare can set strictly necessary cookies for abuse protection, and a service worker can cache static files in your browser storage.
Everything in the table below stays in your browser until you clear site data. The Privacy Policy and the Cookie Policy describe the same list.

Every browser storage key this site writes, what it holds, how much it keeps, and what triggers it
Storage key	What it holds	Limit	Trigger
simply-tools-theme	Light or dark theme choice	One value	Written on every page view
simply_tools_favorites	IDs of tools you marked as favorites	No fixed limit	Written when you click the favorite control
simply_tools_recent	IDs of the tools you opened	Last 10	Written on every tool page view
simple-calc-history	The expressions you typed and the results they produced	Last 20	Written when a Simple Calculator calculation finishes, on an operator key or on equals

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Frequently asked questions

Does the monthly deposit land at the start or the end of the month?

At the end. Each period compounds the running balance first and then adds that period share of your monthly deposit, which is the ordinary end-of-period convention. Switching the compounding frequency between monthly and annually changes how often the interest is applied, not the yearly deposit total.

Why is my loan total so much larger than the amount I borrowed?

A monthly payment has to cover the interest due that month before it reduces what you owe, so a long term at a high rate pays a lot of interest on the way down. The calculator solves the payment from the principal, the monthly rate, and the number of payments using the standard fixed-rate amortization formula, and at a 0% rate it splits the principal evenly across the term instead.

What is the difference between CAGR and the gain printed on my statement?

A statement shows the total change across the whole period. CAGR spreads that change across the years as a geometric average, which is the figure you can compare with an index or with another holding of a different length. The calculator needs a starting value above 0, an ending value above 0, and a duration between 0.1 and 100 years; outside that range it returns no result rather than a wrong one.

Does changing the currency convert my money?

No. Where a selector exists, it only changes the symbol printed next to each figure, and no exchange rate is applied to the arithmetic. The Compound Interest and Loan calculators offer USD, EUR, GBP, and UAH, while the Percentage and Discount calculators add CAD, AUD, and JPY. The CAGR Calculator and the Simple Calculator have no currency selector at all.

Does the loan calculator show a month-by-month amortization schedule?

It does not. It returns the monthly payment, the number of payments, the total paid, and the total interest. For the split between principal and interest in one specific month, the amortization table your lender gives you is the source to use.

Is there an account to create?

No. There is no account system on this site and no calculator asks for one. Every visit to a tool page also adds the ID of that tool to the simply_tools_recent list in the table below, which holds tool identifiers, never anything you typed. The Simple Calculator is the only one of the six that also keeps what you calculated: the last 20 expressions and results, clearable from the tool itself.

Are these results investment advice?

They are arithmetic on the numbers you enter. None of these calculators models taxes, fees, currency conversion, or a rate that changes over time, and none of them predicts what an investment will do.

Run the numbers on your own situation

Open the compound interest calculator and change one number: the year-by-year table updates as you type, so you can see which assumption is doing the work.

Open Compound Interest Calculator