Loan Calculator Guide
When taking out a mortgage, auto loan, or personal loan, calculating your monthly payment and total interest in advance helps with planning. This guide explains how loan interest is calculated and how to use a loan calculator.
How Loan Interest is Calculated
Basic Concepts
- Principal: The amount borrowed
- Interest rate: Annual interest rate (e.g., 3.5% = 0.035)
- Term: Loan period (years or months)
Monthly Interest Rate
Convert annual rate to monthly rate:
Monthly rate = Annual rate ÷ 12
e.g., 3.5% annual → 0.2917% monthly
Equal Payment vs Equal Principal
Equal Payment (Amortization)
You pay the same amount each month.
Characteristics:
- Interest dominates early; principal share increases over time
- Fixed monthly payment makes budgeting easier
- Total interest may be higher than equal principal
Best for:
- Those who prefer fixed monthly expenses
- Mortgages (often use equal payment)
Equal Principal
You pay the same principal each month plus interest on the remaining balance.
Characteristics:
- Higher payments early, decreasing over time
- Total interest is lower than equal payment
- Requires more cash flow at the start
Best for:
- Minimizing total interest
- When you have extra funds early on
How to Calculate Monthly Payments
Equal Payment Formula (PMT)
Monthly payment = P × [r(1+r)^n] / [(1+r)^n - 1]
P: principal, r: monthly rate, n: number of months
Equal Principal Calculation
Monthly principal = Total principal ÷ Number of months
Monthly interest = Remaining balance × Monthly rate
Monthly payment = Monthly principal + Monthly interest
How to Use UnterGletscher Loan Calculator
Key features:
- ✅ Choose equal payment or equal principal
- ✅ Enter principal, interest rate, and term
- ✅ Automatic monthly payment and total interest
- ✅ Amortization schedule display
- ✅ No sign-up required
- ✅ No personal data collection
Use cases:
- Check mortgage monthly payment
- Compare auto loan interest
- Plan personal loan repayment
Try it now: Use Loan Calculator
Tips for Loan Planning
1. Leave Room in Your Budget
A common rule is to keep monthly payments under 40% of income.
2. Compare Rates
Compare rates from multiple lenders and consider fixed vs variable rates.
3. Early Repayment
Check for prepayment penalties and consider paying down principal when you have extra funds.
Conclusion
A loan calculator helps you plan by showing monthly payments and total interest in advance. Use UnterGletscher's free loan calculator for your planning.