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Not investment advice. Educational reading. See Disclaimer.
L.3 · INTERMEDIATE · 2 MIN

Mortgage Mechanics for Investors

Mortgages are the most common financial instrument in America — over $13 trillion outstanding. Understanding how your payment is calculated gives you an edge in both personal finance and real estate investing.

Quiz · 5 questions ↓
§ 01
Monthly Payment = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
§ 02

In the early years of a 30-year mortgage, most of your payment goes to interest. A $400K loan at 6.5% pays ~$2,528/month — but in month 1, $2,167 is interest and only $361 is principal.

§ 03
Use the calculator above to see how a 1% rate change affects your monthly payment. On a $400K loan, the difference between 5.5% and 6.5% is about $250/month ($90K over the life of the loan).
§ 04
You take a $500K, 30-year mortgage at 7%. Your total payments over 30 years will be approximately:
§ 05

The amortization schedule is front-loaded with interest. This is why making extra principal payments early in the mortgage term has an outsized impact — you’re reducing the base on which decades of interest compounds.

§ 06
You have a $500K mortgage at 3.5% (30yr, fixed) with 25 years remaining. Current rates: 7%. Should you prepay from excess cash?
Five questions · AI feedback

Sit with the ideas.

A couple earns $12,000/month gross and wants to buy a $500,000 home with 10% down. Their other debts total $1,200/month. The mortgage rate is 7% for 30 years. What is their monthly mortgage payment (approximately), and will they pass a 43% DTI test?

Why:
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