I Owe $170K on My Mortgage at 0.6% Interest. Here's Why I Won't Pay It Off Early

I want to pay this thing off. Every time I open the banking app and see ¥25 million ($170K) in remaining balance, something in my chest tightens. Eight years of this mortgage and that feeling hasn’t faded one bit. But I don’t pay it off. The 0.6% interest rate keeps overruling my emotions.

This is the full story of eight years with a Japanese mortgage — getting rejected for life insurance because of a therapy visit, refinancing to escape a bad deal, and the never-ending internal debate between “pay it off and breathe” and “invest the difference and get rich slower.”

Eight Years Ago: A ¥30 Million Mortgage

I took out a ¥30 million ($200K) mortgage eight years ago.

The plan was to go with MUFG — Japan’s biggest bank. Rate looked fine, megabank reliability, all that. Mortgage approval in Japan works like you’d expect: income, employment history, credit checks. Pretty standard stuff. But then something I never saw coming happened.

The life insurance screening.

A Therapy Visit Killed My Insurance Approval

Here’s something most non-Japanese readers won’t know: in Japan, every single mortgage requires something called “danshin” — group credit life insurance. If you die, the insurance pays off the remaining mortgage. No danshin approval, no mortgage. Period.

A few years before buying the house, I’d gone through a rough patch at work and visited a psychosomatic medicine clinic. These clinics are common in Japan — somewhere between a therapist and a psychiatrist, people go for stress, insomnia, mild anxiety. I thought of it as a minor thing. Went a few times, felt better, moved on.

Turns out, that “minor thing” shows up in insurance screenings. I got rejected for standard danshin.

The gut punch wasn’t the rejection itself. It was what the rejection meant. In my head, I’d been a little stressed at work. In the insurance company’s eyes, I was a risk. Having that gap between self-perception and institutional judgment laid out in black and white — yeah, that stung.

If there’s one sentence I want people to take away from this article, it’s this: get your mortgage while you’re healthy. Seriously. A casual doctor visit can haunt you for years in mortgage applications.

MUFG vs Sony Bank: The 0.1% That Mattered

When standard danshin isn’t an option, you move to “wide danshin” — a version with relaxed health requirements but a rate surcharge. Think of it like high-risk auto insurance, but for your mortgage life insurance.

MUFG’s wide danshin: +0.3% surcharge. Sony Bank’s: +0.2%.

Just 0.1% difference. But on ¥30 million over 30+ years, that gap adds up to hundreds of thousands of yen. Sony Bank’s base variable rate at the time was 0.45%, so even with wide danshin it came to 0.65%. Cheaper than MUFG. Easy choice.

One catch though: wide danshin stripped away optional coverage like cancer protection. Standard danshin lets you add those. Wide danshin doesn’t. Didn’t think much of it at the time. It nagged at me more and more later.

Then Sony Bank’s Rate Hit 0.9%

Variable rates vary. Obvious statement, but after decades of zero/negative rates in Japan, everyone kind of forgot. The Bank of Japan has been raising rates since 2024 — ending an era of basically free money — and Sony Bank’s variable rate climbed to 0.9%.

Double what I’d started at. Add wide danshin’s 0.2% and I’m at 1.1%. With no cancer coverage. Not great.

That’s when I started looking at refinancing. PayPay Bank (yes, named after the payment app) had a refinancing campaign with competitive rates. But the real prize wasn’t the rate.

It was the chance to qualify for standard danshin.

Years had passed since my clinic visits. Danshin disclosure forms ask about medical history within a specific lookback period — typically 3-5 years. I was outside that window. Applied for standard danshin and… got approved. Just like that.

I can’t overstate how good that felt. That “unstable person” label from eight years ago — gone. Honestly, the approval mattered more to me than the rate savings.

After refinancing, my rate at PayPay Bank is about 0.6%. Standard danshin, so I could add cancer coverage and other options. The psychological relief of escaping Sony Bank’s 0.9% + wide danshin constraints was massive.

Current balance: roughly ¥25 million ($170K). Monthly payment: about ¥85,000 ($560).

0.6% Debt vs 6-8% Index Fund Returns

Here’s the real question. Should I prepay?

My brain knows the answer. There’s almost zero mathematical case for rushing to repay a 0.6% loan. Global index funds (I hold a mix of MSCI All Country and S&P 500) average 6-8% annual returns over the long term. If I threw ¥5 million ($35K) at the mortgage, I’d save about ¥30,000 ($200) per year in interest. That same ¥5 million in index funds? Expected return of ¥300,000-400,000 ($2,000-2,700) per year. More than 10x the difference.

Sure, investing isn’t guaranteed. A 2008-style crash could wipe out 40% in a single year. But over 15-20 year horizons, the probability of a diversified index beating 0.6% is overwhelmingly high. Eight years of actual index investing have reinforced my confidence in this bet.

I’ve started thinking of my mortgage as the cheapest leverage I’ll ever get. Where else can an individual borrow $170K from a bank at 0.6%? Nowhere. So I frame it as a real estate investment with absurdly cheap financing. Partly genuine conviction, partly me tricking myself into being okay with the debt. But as long as the numbers hold up, I’m sticking with it.

Diverting investment money to prepay a sub-1% loan? That’s leaving money on the table. This rate is a gift. I’m going to use it.

The 2% Threshold — But That World Looks Nothing Like Today

So what rate would make me consider prepaying?

Gut feeling: around 2%. There’s something psychological about crossing into “2-point-something” territory. The monthly payment impact becomes tangible, and the word “debt” starts weighing heavier.

But here’s the thing I keep reminding myself: a world where mortgage rates hit 2% is a completely different world from today. Savings account yields would be way higher too. Cash sitting in a regular deposit would actually earn something meaningful. In that scenario, keeping cash liquid might be better than prepaying.

Index fund returns could shift too. Higher rates mean different market dynamics. The version of me sitting at 0.6% today shouldn’t be making rigid rules for a 2% future.

So my conclusion is… no conclusion. More like a permanent bookmark. As I wrote in my piece about the interest rate shift, in a world where rates actually move, “check the numbers at the time” beats “follow the rule I set years ago.”

Get Your Mortgage While You’re Healthy

If I could talk to myself eight years ago, I’d say it louder: get your mortgage while you’re healthy.

A few casual visits to a stress clinic — that’s all it took. Couldn’t get standard life insurance. Got stuck with wide danshin at a higher rate. Lost access to cancer coverage add-ons. Carried that penalty for years.

For anyone reading this who’s thinking about buying a house and has any health concerns: mortgage screening doesn’t just look at your income and employer. It looks at your medical history. A visit you thought nothing of can come back to bite you years later. In Japan’s system, that’s just how it works.

When I finally got approved for standard danshin a year ago, I was genuinely relieved. But flip that around — it means I’d been paying an unnecessary premium for years. The 0.2% wide danshin surcharge on ¥30 million is about ¥60,000 ($400) per year. Over seven years, that’s ¥420,000+ ($2,800+). The cost of a few therapy sessions, compounded across a decade of mortgage payments.

This Tug-of-War Probably Never Ends

Will I ever stop debating whether to prepay? Probably not. As long as the rate stays at 0.6%, my brain says “don’t prepay” and my gut says “just make it go away.”

Monthly ¥85,000 payments, surplus cash into index funds. The spreadsheet says this is correct. But seeing ¥25 million in outstanding debt and thinking “life would be simpler without this” — that happens more often than I’d like to admit. Debt is debt, no matter how cheap.

There’s no clean answer to this tug-of-war. I don’t think there ever will be.

But maybe that’s just what having a mortgage is like.

This article reflects personal experience and is for informational purposes only — not investment advice. All investment decisions are your own responsibility.