Home buying

What does a 0.5% rate change actually cost you?

By A. Ledger · 8 min read

When mortgage rates tick up half a point, the headline number sounds small. The monthly difference is what bites. Rather than make you trust my arithmetic, here's the actual calculation — and you can change the numbers yourself. It's a live Instacalc embed.

Monthly payment — edit any number

principal = $400,000 annual rate = 6.5% years = 30 monthly rate = annual rate / 12 n = years * 12 payment = principal * monthly rate / (1 - (1 + monthly rate)^-n)

Now nudge the rate to 7.0% and watch the payment jump. Over thirty years that gap compounds into real money. Here's the same calculation in a dark theme, which the embed supports with a single attribute:

Same calc, dark theme

principal = $400,000 rate_low = 6.5% rate_high = 7.0% monthly_low = principal * (rate_low/12) / (1 - (1 + rate_low/12)^-360) monthly_high = principal * (rate_high/12) / (1 - (1 + rate_high/12)^-360) extra_per_month = monthly_high - monthly_low extra_over_30y = extra_per_month * 360

Want to run your own numbers from scratch? Open a blank calc with the figure already typed in: open this payment formula in Instacalc →

Why embed instead of screenshot?

A screenshot of a number is dead the moment rates move. A live embed lets every reader plug in their loan size and their rate. That's the whole point — the math stays honest because the reader can check it.