$ Finance Guide

Complete Guide to Finance, Loans, and Investment Calculations

Understand interest rates, amortization schedules, compound growth, and debt management.

31 free calculatorsFormula includedWorked example
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📚 Overview

Financial calculations are the bedrock of personal wealth and business sustainability. Whether you are taking out a mortgage, paying off credit cards, or investing in the stock market, understanding how time and compound interest affect your money allows you to save thousands in borrowing costs and maximize compounding returns.

📐 Compound Interest & Monthly Amortization Formula
A = P(1 + r/n)^(nt) and M = P [ r(1 + r)^n ] / [ (1 + r)^n - 1 ]

Where P is the initial principal balance, r is the annual interest rate, n is the number of times interest compounds per year, t is time in years, and M is the monthly amortization payment.

🔢 Worked Example

Scenario: Borrowing a $20,000 vehicle loan at 6% annual interest over a 5-year repayment term (60 months).

  • Principal: $20,000
  • Annual Interest: 6.0% (0.005 monthly)
  • Term: 60 months
  1. Monthly rate r = 0.06 / 12 = 0.005
  2. Numerator = 20,000 × [0.005 × (1.005)^60] = 20,000 × [0.005 × 1.34885] = $134.885
  3. Denominator = (1.005)^60 - 1 = 1.34885 - 1 = 0.34885
  4. Monthly payment M = 134.885 / 0.34885 = $386.66
Your monthly payment is $386.66. Over 5 years you pay $23,199.36 in total, including $3,199.36 in interest.
💡 Pro Tips
  • Making one extra monthly payment per year can shave several years off a 30-year home mortgage.
  • Always distinguish between APR (annual percentage rate) and APY (annual percentage yield, which factors in compounding).
  • Prioritize paying down high-interest revolving credit before investing in assets yielding lower returns.
  • Use our Loan and Mortgage calculators to compare bi-weekly vs monthly payment schedules.
🧮 Finance Calculators (31)

Put the formulas above into practice with these free tools:

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Loan Payment Calculator

Monthly payment, total cost, and interest.

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Compound Interest Calculator

See how savings grow with monthly compounding.

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Simple Interest Calculator

Interest earned without compounding.

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Discount Calculator

Find the sale price and how much you save.

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Sales Tax Calculator

Tax amount and total price at checkout.

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ROI Calculator

Return on investment as a percentage.

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Profit Margin Calculator

Margin, markup, and profit from revenue and cost.

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Mortgage Calculator

Monthly mortgage payment from price, down payment, and rate.

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Savings Goal Calculator

How much to save each month to reach a goal.

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Inflation Calculator

What prices or savings will be worth after years of inflation.

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VAT Calculator

Add or remove VAT from a price.

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Hourly to Salary Calculator

Turn an hourly wage into daily, weekly, monthly, and yearly pay.

View all 31 tools →
❓ Frequently Asked Questions
What is the difference between simple and compound interest?

Simple interest is calculated only on the initial principal. Compound interest is calculated on the principal plus all interest accumulated from prior periods, accelerating growth over time.

How does amortization work?

With amortized loans, early payments consist mostly of interest with a small principal reduction. As the balance decreases over time, a growing share of each payment goes directly toward reducing principal.

What is the 50/30/20 budgeting rule?

A classic budget framework: allocate 50% of your after-tax income to essential needs, 30% to flexible wants, and 20% to savings and debt repayment.