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 at 6.5% = 6.5% rate at 7.0% = 7.0% monthly at 6.5 = principal * (rate at 6.5%/12) / (1 - (1 + rate at 6.5%/12)^-360) monthly at 7.0 = principal * (rate at 7.0%/12) / (1 - (1 + rate at 7.0%/12)^-360) extra per month = monthly at 7.0 - monthly at 6.5 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.