Economy/Finance Calculator

Interest Calculator

Compound Interest (Total Amount) Calculator

Compound interest adds accrued interest back to the principal each period, so interest is ...

Simple Interest Calculator

Simple interest is calculated only on the principal. With the principal, annual rate, and ...

US Savings Tax at Maturity Calculator

Estimate federal and state income tax on savings interest when tax is applied once at the ...

US Savings Tax Withheld Calculator

Estimate tax on savings interest as it accrues, using a combined federal and state margina...

Equal Principal & Interest Payment Calculator

Equal principal and interest repayment pays a fixed amount of principal plus interest each...

Equal Principal Payment Calculator

Equal principal repayment pays a fixed principal amount each month plus the interest accru...

Average Purchase Price Calculator

When buying stocks or crypto in multiple tranches, the average purchase price calculator h...

Return on Investment (ROI) Calculator

ROI is the ratio of profit to the amount invested and is widely used to compare investment...

US Sales Tax Calculator

Estimate US state and local sales tax. Enter a pre-tax price and your combined rate (defau...

Currency Converter Calculator

Multiply a foreign amount by the exchange rate to get the local currency amount. Useful fo...

Margin Rate Calculator

Enter cost and selling price to calculate the margin (profit) and margin rate (%) at the s...

About This Category

This category answers the money questions that come up between payslips: how much sales tax is added to a price, what a loan really costs, and what a deposit is worth after tax. Every tool uses the formula banks and accountants use, with inputs and outputs labelled in matching units so the result can be checked by hand.

Start from what you already know. Given a total amount, the sales tax calculator works backwards to the pre-tax figure; given a rate and a term, the loan tools split each payment into interest and principal. The investing tools then turn several purchases into a single average price or return, which is what comparisons actually require.

Frequently Asked Questions

Should I use simple or compound interest?

Use simple interest for instruments where the interest itself earns nothing, such as promissory notes and flat-rate car finance. Use compound interest for deposits and savings, where interest is credited to the balance: at 5 % the difference after ten years is about 129 per 1,000 invested.

Why do two loans at the same rate cost different amounts?

Because the repayment structure changes the balance over time. Equal-principal repayment clears capital faster and therefore pays less total interest, while equal-payment keeps the instalment flat and front-loads interest. Same nominal rate, different total cost.

Do the calculators include fees and taxes?

Only the values you enter. For the real cost, add arrangement fees to the amount borrowed and enter the after-tax interest rate, since a 1 % fee on a five-year loan adds roughly 0.2 percentage points to the effective annual rate.

Calculators in This Category

Sources & last update

2026-10-19