Mortgage Calculator

What this tool does

Enter your loan amount, annual rate, and years. The tool calculates equal payment (annuity) and equal principal side by side: monthly dues, total paid, total interest, and a chart that shows how payments change over time.

Two repayment styles, kid-friendly

• Equal payment (annuity): pay the same amount every month. Early months are mostly interest; later months are mostly principal.
• Equal principal: split the principal evenly across all months; interest is charged on the shrinking balance, so the payment keeps going down. Heavier at the start, cheaper overall.

Think of it as “smooth and steady” versus “front-loaded but cheaper.”

Which costs less overall?

• Total interest: equal principal always wins because the balance falls faster.
• Monthly burden: equal payment is smooth; equal principal starts high and eases off every month.

When to choose which?

• Need predictability and tight cash flow → equal payment.
• Can handle a heavier start and want to pay less interest → equal principal.
• Higher rates or longer terms make the gap bigger; low rates or short terms make the two closer.

Example (1,000,000 loan, 4.2% APR, 30 years)

• Equal payment: about 4,890 every month; total paid ≈ 1.76M; interest ≈ 760k.
• Equal principal: first month ≈ 6,278, last month ≈ 2,788; total paid ≈ 1.63M; interest ≈ 632k.

Equal principal saves roughly 130k in interest but needs more cash up front.

How to use the tool

1. Enter the loan amount, years, and annual rate (slide or type).
2. Check the two cards on the right to see monthly dues and totals for each method.
3. The chart shows monthly payments over time: green is flat (equal payment), blue slopes down (equal principal).
4. Read the short tips below to confirm which style fits your situation.

Tips

• The amount is the loan portion (after down payment).
• Try different rates/terms to see how the gap changes.
• If rates might rise later, leave yourself a buffer when picking a plan.