Japan's Hidden Mortgage Trap: The 5-Year Rule That's Not What You Think (And Why US ARMs Are Actually Simpler)

The average price of a used condo in Tokyo’s 23 wards hit ¥120 million ($800,000) in February 2026.

I bought mine for ¥35 million ($233,000) eight years ago. Even then, I thought it was expensive. Spent weeks looking at places between ¥30–50 million, trying to convince myself it was a reasonable purchase.

That ¥35 million is now ¥120 million. A 3.4x increase. Doesn’t feel real.

And variable mortgage rates — which is what about 80% of Japanese borrowers have, including me — just crossed 1% for the first time in 15 years. When I signed my mortgage in 2018, I got 0.45%.

Condo prices up 3.4x. Interest rates more than doubled. If you’re buying now, or already on a variable rate… there’s something you should understand about how Japanese mortgages actually work.

Quick Japan Context (For Non-Japanese Readers)

Japanese variable-rate mortgages work very differently from US adjustable-rate mortgages (ARMs). If you’re familiar with US ARMs, file this under “interesting financial oddities” and read on.

US ARM: Rate can adjust periodically (e.g., annually after a fixed period). When the rate changes, your monthly payment changes immediately. Transparent, painful, but at least honest.

Japanese variable-rate mortgage: Rate reviews happen every 6 months, but your monthly payment is locked for 5 years regardless. Instead of adjusting the payment, the split between interest and principal silently shifts. More of your payment goes to interest, less to principal. Your balance barely moves. This is called the “5-Year Rule.”

On top of that, the “125% Rule” caps any payment increase to 125% of the previous amount — even after the 5-year lock ends. Sounds nice? Actually, it’s a way to defer the problem until the end of the loan term, when you might face a lump-sum payment on the remaining principal plus unpaid interest.

In other words: Japan’s version hides rate increases behind a fixed-payment facade. Most Japanese borrowers don’t fully understand this. I didn’t either, until it bit me.

80% of Borrowers Are on Variable Rates

Japan’s Housing Finance Agency reports that 75–84% of mortgage borrowers chose variable rates. That’s 4 out of 5 people.

Here’s what major banks are charging in April 2026:

Bank	Variable Rate (Best Rate)
MUFG Bank	0.945%
SMBC	1.275%
Mizuho Bank	1.225–1.675%
PayPay Bank	0.980%
au Jibun Bank	1.134%
SBI Sumishin Net Bank	1.200%

When I refinanced to PayPay Bank, I got 0.6%. New borrowers at the same bank now get 0.98%. Same bank, worse deal. That window closed.

The “5-Year Rule” Nobody Explained to Me

Here’s what I wish someone had told me.

When I borrowed ¥30 million on a variable rate, the bank didn’t explain the 5-year rule. The real estate agent mentioned it in passing. That was it.

Japan’s variable-rate mortgages have two built-in mechanisms: the 5-Year Rule and the 125% Rule. They sound reassuring. They’re not.

The 5-Year Rule: rates are reviewed every 6 months (April and October), but your monthly payment stays fixed for 5 years. Even if rates jump from 0.6% to 1.5%, your bank withdrawal doesn’t change.

Sounds great, right? Here’s the catch.

The payment amount stays the same, but what’s inside changes. More goes to interest, less to principal. You’re paying every month, but your loan balance barely moves. In extreme cases — if rates spike high enough — your monthly payment can’t even cover the interest. That’s called “unpaid interest.” You’re making payments, and your debt is growing. Nightmare stuff.

The 125% Rule Isn’t a Safety Net Either

After 5 years, your payment gets recalculated. But the increase is capped at 125% of your previous amount.

If you were paying ¥150,000/month, the max becomes ¥187,500. No sudden doubling.

But this is just deferral. Whatever principal you didn’t pay gets pushed to the back. When your 35-year term ends, everything left — principal plus unpaid interest — is due in a lump sum.

The 5-year rule and 125% rule are shock absorbers. They don’t reduce your debt. Think of it like an adjustable-rate mortgage (ARM) in the US, but with the rate changes hidden behind a fixed payment facade.

My Bank Didn’t Even Have the 5-Year Rule

Here’s where it gets personal.

I originally borrowed from Sony Bank at 0.45% variable (plus 0.2% for expanded life insurance, so 0.65% effective). Later, Sony Bank’s rate rose to 0.9%. With insurance: 1.1%.

What I noticed was simply: “Wait, my payment went up. When did that happen?”

Turns out Sony Bank doesn’t apply the 5-year rule or 125% rule. Rate increases hit your payment immediately. I had no idea.

SBI Shinsei Bank is the same way. If you’re on a variable rate, check whether your bank applies these rules. Right now.

I eventually refinanced to PayPay Bank at 0.6%, got approved for standard life insurance (couldn’t before due to mental health history), and dropped the extra ¥60,000/year surcharge. That was a good move.

What Happens When Rates Go to 2%

The Bank of Japan’s policy rate is currently 0.75%. Nomura Securities’ main scenario has it reaching 1.5% by 2027. Variable mortgage rates could climb to 1.5–2.5%.

Here’s what that looks like for different loan amounts. Starting rate: 0.5%, 35-year term, rate change at year 5.

¥50 Million Loan (~$333K, typical for eastern Tokyo)

Rate at Year 5	Monthly Payment	Monthly Increase	Annual Impact
0.5% (unchanged)	¥129,793	—	—
1.5%	¥149,718	+¥19,925	+¥239K
2.0%	¥160,346	+¥30,554	+¥367K

¥70 Million Loan (~$467K, typical for southern/western Tokyo)

Rate at Year 5	Monthly Payment	Monthly Increase	Annual Impact
0.5% (unchanged)	¥181,710	—	—
1.5%	¥209,605	+¥27,896	+¥335K
2.0%	¥224,485	+¥42,775	+¥513K

On a ¥70 million loan, a rate increase to 2% means an extra ¥42,775 per month. That’s ¥513,000 per year — roughly $3,400 — straight out of your take-home pay.

And central Tokyo’s average (Chiyoda, Chuo, Minato wards) is ¥160 million for 70m². At those numbers, the impact is even more brutal.

Low Rates Inflated Prices. Now Both Are Rising.

When I bought in 2018, rates were around 0.4–0.5%. Low rates meant low monthly payments, which meant people could “afford” higher-priced properties. Real estate agents knew this. Prices got pushed up because the monthly math still worked.

Low rates, high prices. It felt like a wash.

But now? Rates are up AND prices are up. Both dials turned the wrong way at the same time.

My honest opinion: this isn’t a great time to buy in Tokyo. For prices to make sense, they need to come down as rates go up. Otherwise the math just doesn’t work for regular working people.

But I also know that people said “don’t buy now” in 2018, and my ¥35 million condo might be worth ¥45–50 million today. Real estate timing is, to use the technical term, a gamble.

The only safe rule: buy what you can afford if rates hit 2%. Not what you can afford at today’s rate.

Three Things Variable-Rate Borrowers Should Do Now

For those already on a variable rate — here’s what I actually do.

First: check whether your bank applies the 5-year rule. Sony Bank and SBI Shinsei don’t. I learned this the hard way.

Second: watch fixed-rate trends. When the gap between variable and fixed narrows enough, it’s time to consider refinancing. The gap is shrinking.

Third: set your own “trigger point” for prepayment. Mine is: reconsider at 2%, seriously evaluate lump-sum prepayment at 3%. Having a rule prevents anxiety-driven decisions every time rates tick up.

Know the Rules, Watch the Numbers

Eight years ago I bought at ¥35 million, variable rate 0.45%. Rate went up to 0.9% without me noticing. Refinanced to 0.6%. Could go up again.

Whether that was the right call — honestly, I’ll only know in retrospect.

But the version of me who didn’t understand the 5-year rule, and the version who does, will handle the next rate increase very differently.

Real estate and interest rates are unpredictable. That’s exactly why you learn the rules and watch the numbers. For a regular salaryman like me, that’s really all there is to do.

The Broader Lesson

If you’re reading this from outside Japan, the specific rules don’t apply to you. But the meta-lesson does: never sign a long-term financial product without understanding the mechanisms behind “safety features.”

Banks everywhere sell the same story: “We’ll protect you from rate shocks.” In the US, teaser rates. In Japan, the 5-year rule. In the UK, fixed-term arrangements with brutal reversion rates. The marketing language is reassuring; the actual math is rarely so.

If I could rewind 8 years, I wouldn’t necessarily choose a different mortgage. But I would have read the actual mechanism, not the sales brochure. Japanese borrowers are discovering this now, at scale, as rates climb. Wherever you’re from, ask the awkward question: “What happens if rates go to 2x what they are today?” If the answer makes you uncomfortable, the product is probably structured against you.

This article reflects personal experience and research, not financial or real estate advice. Please consult professionals for decisions specific to your situation.