Is my financial data sent anywhere?

No. Every calculator runs as JavaScript in your browser. Income, balances, card numbers and account identifiers are never transmitted, never logged and never stored on a server. There is no account and no email capture, and the tools continue to work with the network disconnected.

Is it safe to enter a real card number into the validator?

The validation is a Luhn checksum computed locally and the number is never sent anywhere — so technically yes. As a general habit, though, avoid entering live card numbers into any website, including this one. For testing, use the published test numbers from Stripe or Adyen instead.

Which country’s tax rules do the tax tools use?

Each tax tool lets you select a jurisdiction and states which rules and tax year it is applying. They model the main bands and standard allowances only. Regional variation, filing status, deductions, credits and reliefs are not covered, and any of those can change the result substantially.

Is this financial advice?

No. These are calculators — they compute what you enter and nothing more. They cannot account for your circumstances, tax position, risk tolerance or goals, and no figure here should be treated as a recommendation. For decisions of consequence, consult a qualified financial adviser or tax professional in your jurisdiction.

Why does my bank’s EMI differ from the calculator’s?

Usually fees rather than a maths error. Lenders add processing fees, insurance and sometimes documentation charges to the advertised rate, and some use a different day-count convention or round the instalment up. Compare the APR — which is required to include most fees — rather than the headline interest rate.

Finance Calculators — Loans, Investments, Tax & Payments

Finance calculators that run entirely in your browser — your salary, balances and card numbers never leave the device.

39 tools · Reviewed by Mimamsa, Founder & Engineer, CodeLint.Dev

Financial tools have a privacy problem that developer tools do not. Working out whether you can afford a mortgage means entering your income, your savings and your debts. Most calculators send all of it to a server, and a good number are lead-generation forms wearing a calculator’s clothes — the real product is your contact details, sold onward to a broker.

None of these calculators transmit anything. The arithmetic runs in JavaScript on your own machine, there is no account, no email capture, and no partner network. You can disconnect from the network and every one of them keeps working.

The methods are conventional and stated on each page: reducing-balance amortisation for loans and mortgages, compound growth with configurable compounding frequency for investment projections, and standard bracket arithmetic for the tax estimators. Where a calculation depends on a jurisdiction — tax bands, capital-gains treatment, GST and VAT rates — the page says which one it is using and as of when.

One thing these are not: financial advice. They are arithmetic, and arithmetic cannot know your circumstances. Tax rules in particular change annually, vary by region within a country, and turn on details no general calculator can capture. Use these figures to understand the shape of a decision, then confirm anything that matters with a qualified professional.

Currency & crypto

Currency Converter Convert between world currencies at current reference rates, with a conversion table for common amounts.Exchange Rate Tracker Track a currency pair over time to see the trend behind today’s rate.Crypto Price Tracker Current prices for major cryptocurrencies against fiat, with change over common intervals.Crypto Unit Converter Convert between bitcoin and satoshis, ether, gwei and wei — where an order-of-magnitude slip is expensive.

Loans & credit

Loan EMI Calculator Monthly instalment, total interest and a full amortisation schedule for any principal, rate and term.Mortgage Calculator Repayments including taxes and insurance, with the effect of overpayments on term and total interest.Compound Interest Calculator Growth over time with configurable compounding frequency and optional regular contributions.Simple Interest Calculator Flat interest on principal — the basis of many short-term and informal loans.Credit Score Estimator Estimate how the standard scoring factors combine, and which ones move a score most.Debt Payoff Planner Compare avalanche and snowball strategies across multiple debts by total interest and time to clear.

Investment & returns

SIP Calculator Project the value of regular monthly investments at an assumed rate of return.CAGR Calculator Compound annual growth rate between two values — the figure that makes returns comparable across periods.ROI Calculator Return on investment in absolute and annualised terms, so holding periods can be compared fairly.Stock Profit & Loss Position outcome including brokerage and fees, with the break-even price shown.Dividend Yield Calculator Yield on cost and current yield, plus projected income at a given holding size.Portfolio Allocation Current versus target weights across holdings, with the trades needed to rebalance.

Personal finance

Budget Planner Allocate income across categories using 50/30/20 or a custom split, with the shortfall shown.Net Worth Calculator Assets minus liabilities, itemised, to give a single figure and a picture of its composition.Retirement Calculator Project a retirement pot from current savings, contributions and expected return, against a target income.Emergency Fund Calculator How many months of expenses to hold, based on income stability and fixed commitments.Expense Ratio Impact What a fund’s annual fee costs over a full holding period — usually far more than it appears.Tip & Bill Splitter Split a bill with tip across any number of people, evenly or by individual share.

Business & accounting

Invoice Generator Create a printable invoice with line items, tax and totals — generated locally, no account required.Markup & Margin Calculator Convert between markup and margin, the two figures most often confused when pricing.Break-Even Calculator Units and revenue required to cover fixed and variable costs at a given price.Cash Flow Estimator Project monthly inflows and outflows to find the point where the balance goes negative.Depreciation Calculator Straight-line, declining-balance and sum-of-years-digits schedules for an asset.Runway Calculator Months of runway from cash balance and burn rate, with the effect of a change in either.

Payments & validation

Card Number Validator Luhn check and card-network identification. Runs locally — no card number is transmitted.BIN Lookup Identify the issuing bank, network, card type and country from a bank identification number.IBAN Validator Validate an IBAN’s structure, length and mod-97 checksum, per country.IBAN & SWIFT Formatter Format account identifiers into their correct printed grouping for either standard.SWIFT / BIC Lookup Decode a BIC into its bank, country, location and branch components.UPI ID Validator Check the format of an Indian UPI virtual payment address against its provider’s pattern.Payment Fee Comparator Compare processor fees on a given transaction volume and average ticket size.

Tax

Income Tax Estimator Estimate income tax across bands for a chosen jurisdiction, with effective and marginal rates shown.Capital Gains Tax Estimate gains tax with short- and long-term holding treatment separated.GST / VAT Calculator Add or extract GST and VAT at any rate, in both the inclusive and exclusive directions.Tax Bracket Lookup Current income tax bands by country, showing where a given income falls.

Markup or margin?

These two get transposed constantly, and the gap widens fast at higher rates. Both describe the same £40 profit on a £100 sale that cost £60:

Measure	Formula	On cost 60, price 100
Markup	(price − cost) ÷ cost	66.7%
Margin	(price − cost) ÷ price	40.0%
—	A 100% markup is a 50% margin	They converge only at zero

In-depth guides

Long-form articles covering the standards and formulas behind these tools.

Frequently asked questions

Is my financial data sent anywhere?: No. Every calculator runs as JavaScript in your browser. Income, balances, card numbers and account identifiers are never transmitted, never logged and never stored on a server. There is no account and no email capture, and the tools continue to work with the network disconnected.
Is it safe to enter a real card number into the validator?: The validation is a Luhn checksum computed locally and the number is never sent anywhere — so technically yes. As a general habit, though, avoid entering live card numbers into any website, including this one. For testing, use the published test numbers from Stripe or Adyen instead.
Which country’s tax rules do the tax tools use?: Each tax tool lets you select a jurisdiction and states which rules and tax year it is applying. They model the main bands and standard allowances only. Regional variation, filing status, deductions, credits and reliefs are not covered, and any of those can change the result substantially.
Is this financial advice?: No. These are calculators — they compute what you enter and nothing more. They cannot account for your circumstances, tax position, risk tolerance or goals, and no figure here should be treated as a recommendation. For decisions of consequence, consult a qualified financial adviser or tax professional in your jurisdiction.
Why does my bank’s EMI differ from the calculator’s?: Usually fees rather than a maths error. Lenders add processing fees, insurance and sometimes documentation charges to the advertised rate, and some use a different day-count convention or round the instalment up. Compare the APR — which is required to include most fees — rather than the headline interest rate.

Other tool categories

Generators & Utilities Generators and converters for the values you need constantly and should never have to fetch from a server.AI Tools Tooling for the practical questions of building on language models: how many tokens, how much money, which model, and why did the output change.Reference & Data The lookup tables you open a dozen times a week, each searchable and on one page.Date & Time Timers and date arithmetic that stay accurate when the tab is in the background.