Investment Calculators
Eight calculators sounds like a lot until you realise most people only ever need two or three of them. The hard part is not the arithmetic — it is working out which question you are actually asking. Are you projecting what a pot of money becomes, or working backwards from a target you have already set? Are you measuring something that already happened, or modelling something that has not?
This page is built to answer that. Below you will find a decision guide that maps plain-language questions to the right tool, a side-by-side comparison of what each calculator needs and returns, and notes on which ones are worth running together. Every tool is free, needs no sign-up, and runs entirely in your browser.
Which Calculator Do You Need?
Find the question closest to the one in your head, and follow it to the tool that answers it.
| If you are asking… | What you will learn | Go to |
|---|---|---|
| “What will my savings be worth in 20 years?” | Final balance from a lump sum, plus a year-by-year growth path | Compound Interest |
| “If I invest $500 every month, where do I end up?” | Future value of recurring contributions and total invested vs gained | SIP / DCA |
| “Did that investment actually do well?” | Total return, profit or loss, and the annualised rate | ROI |
| “What is this loan really going to cost me?” | Monthly payment, lifetime interest, and a full amortisation schedule | Loan Payment |
| “Am I saving enough to retire?” | Projected corpus at retirement and the monthly saving needed to close a gap | Retirement |
| “Will this money still be worth this much later?” | Purchasing power over time and the real value behind a nominal figure | Inflation |
| “What did I clear on that trade after fees?” | Net profit or loss, break-even price, and position sizing | Stock P&L |
| “How much do I need before I can stop working?” | Your target number under the 4% rule and the timeline to reach it | FIRE Number |
All 8 Calculators
Compound Interest
The foundation tool. Enter a lump sum, a rate and a horizon, then choose how often interest compounds — daily through annually — and watch the gap that frequency makes.
Calculate →Return on Investment
Backward-looking rather than predictive. Compare what you put in against what you got out, and convert a raw percentage into an annualised figure you can fairly compare across holding periods.
Calculate →SIP / Dollar Cost Avg
For money added on a schedule instead of all at once. Uses the annuity formula to separate what you contributed from what the market added on top.
Calculate →Loan Payment Calculator
Compounding pointed the other way. Works for mortgages, car finance and personal loans, and shows how each payment splits between interest and principal.
Calculate →Retirement Planner
Combines what you already hold with what you keep adding. Tells you the projected corpus and, if it falls short, the monthly contribution that closes the gap.
Calculate →Inflation Impact
A reality check on every other projection. Translates a future nominal amount into what it would actually buy in today's money.
Calculate →Stock Profit & Loss
Position-level rather than portfolio-level. Accounts for brokerage on both sides of the trade and gives the break-even price you need to clear costs.
Calculate →FIRE Number
Works backwards from spending rather than forwards from savings. Applies the 4% rule to annual expenses to produce the target that makes work optional.
Calculate →Inputs and Outputs Compared
If you are not sure whether you have the figures a given tool needs, check here before you start.
| Tool | Direction | Key inputs | Main output |
|---|---|---|---|
| Compound Interest | Projects forward | Principal, rate, years, compounding frequency | Final balance |
| SIP / DCA | Projects forward | Monthly contribution, rate, years, optional lump sum | Future value |
| ROI | Measures the past | Amount invested, amount returned, holding period | ROI % and annualised % |
| Loan Payment | Projects forward | Loan amount, interest rate, term | Monthly payment |
| Retirement | Projects and back-solves | Current savings, monthly saving, age, target | Corpus and any shortfall |
| Inflation | Converts value | Amount, inflation rate, years | Real purchasing power |
| Stock P&L | Measures the past | Buy price, sell price, quantity, fees | Net profit or loss |
| FIRE Number | Works backwards | Annual expenses, savings rate, withdrawal rate | Target number |
Calculators That Work Better Together
Most useful answers come from running two tools in sequence rather than trusting one in isolation. A few pairings worth knowing:
- Retirement, then inflation. A projected corpus of $1.5 million is a nominal figure. Run it through the inflation calculator over the same horizon and you will see what it actually buys — at 3% over 25 years, that number's real purchasing power is closer to $716,000. Plans that look comfortable in nominal terms often need revisiting.
- FIRE, then SIP. The FIRE calculator hands you a target. On its own that is just a large, slightly discouraging number. Feed it into the SIP calculator as a goal and you convert it into a monthly contribution, which is the only part you actually control.
- Loan, then compound interest. When there is spare cash and a debt, the question is whether to overpay the loan or invest instead. Compare the lifetime interest saved in the loan calculator against the projected growth of the same money in the compound interest calculator. Whichever figure is larger points to the answer.
- Stock P&L, then ROI. The stock calculator gives you the cash result of one position after fees. The ROI calculator turns that into an annualised percentage, which is the only fair way to compare a three-week trade with a three-year hold.
Frequently Asked Questions
Which investment calculator should I use first?
If you are starting out, use the compound interest calculator. It models the single mechanism — growth on top of previous growth — that every other tool here builds upon. Once you have a feel for how a rate and a time horizon interact, the retirement, SIP and FIRE calculators stop looking like separate tools and start looking like the same idea pointed at different questions.
What is the difference between the compound interest and SIP calculators?
Contribution pattern is the whole difference. The compound interest calculator models a single lump sum left alone to grow. The SIP calculator models money added on a repeating schedule, which needs the future value of an annuity formula because each contribution compounds for a different length of time. Use compound interest for a one-time deposit, SIP when you are paying in every month, and the SIP tool's optional lump-sum field when you are doing both.
Do these calculators account for inflation or tax?
The growth calculators return nominal figures and do not deduct tax. That is deliberate. Tax treatment depends on your account type and country, and a calculator that quietly guessed at it would be more misleading than one that leaves it out. For inflation, run any projection through the inflation calculator to convert it into today's purchasing power — a step worth taking on any projection longer than about ten years.
What rate of return should I assume?
No single figure is right, so it is better to model a range. The S&P 500 has returned roughly 10% per year on average over the long run before inflation, which is why 7–8% is a common post-inflation assumption. Bonds have historically sat nearer 3–5%. Running a conservative, moderate and optimistic scenario tells you far more than one confident number, and every calculator here recalculates instantly so comparing them costs nothing.
Are these calculators free, and is my data stored?
All eight are free with no sign-up and no ads. Every calculation runs in your browser using JavaScript, so the figures you type are never transmitted to a server or saved anywhere. Closing the tab discards them. See the about page for who built the site and why, or the privacy policy for specifics on what is and is not collected.