April 5, 2026· Updated May 13, 2026
By the HalfKey team
August clawback: when the kōnetsuhi flat fee bites back
The kōnetsuhi flat fee bets you'll use an average amount of electricity. August on an eighth-floor west-facing unit isn't average. The contract has a clause that decides who pays the gap.
You book a 60-night Tokyo monthly mansion starting July 20. Rent is ¥210,000 a month. Utilities are bundled at a flat ¥15,000 (the 光熱費 kōnetsuhi, utility line). Cleaning is ¥50,000. Your budget for the stay is ¥720,000.
On August 28 the operator (the company that runs the furnished rental) emails you a supplemental invoice for ¥9,400. It points to clause 14.3 of the contract. It calls the charge a 超過分精算 (chōkabun seisan — overage settlement). The operator didn't invent it that morning. It was in the contract from the day you signed.
The flat fee assumes you'll use an average amount of electricity. An eighth-floor west-facing unit with the AC on 16 hours a day is not average. The clawback clause decides who pays the gap.
Start with what an average month looks like. A 22m² studio with one tenant uses about 220 kWh of electricity in a normal Tokyo August. That's reibō (cooling mode) on for the eight hours you sleep, three more hours after work, plus weekends.
TEPCO's residential 従量電灯B (jūryō dentō B — metered lighting B) tariff, all in, runs about ¥35 per kWh. So 220 kWh × ¥35 = ¥7,700 of electricity. Gas adds ¥3,500. Water adds ¥2,500. Total metered cost: ¥13,700.
At a ¥15,000 flat fee, the operator keeps ¥1,300. On an average August, the bet works.
Now run the bad case. Eighth floor, west-facing, afternoon sun on the concrete. A tenant working from home through the heatwave. AC on 16 hours a day instead of 11. The kWh climbs from 220 to 380. The same tariff applies, but more of those kWh fall in the third pricing tier (¥40 per kWh above 300 kWh).
380 kWh works out to about ¥14,000 of electricity alone. Gas and water unchanged at ¥6,000. Metered total: ¥20,000. The operator's bet was ¥15,000.
The gap: ¥5,000 in one month. Clause 14.3 decides who pays it.
The clause isn't standard. Tokyo monthly mansion contracts run four patterns.
The most common is ceiling-with-overage. "光熱費は月額¥15,000を上限とし、これを超える分は実費請求とする" ("the kōnetsuhi has a monthly cap of ¥15,000; anything above is billed at actual cost"). In English versions: "Utilities are bundled up to a monthly ceiling of ¥15,000. Use above that ceiling is billed at the meter rate."
The number on the listing page is not a flat fee. It's a ceiling on bundled cost. The word "ceiling" never appears on the listing page. The word "flat" does.
A second pattern uses a high-water mark. "電力使用量が月300kWhを超える場合、超過分を東京電力料金表に基づき請求" ("if monthly electricity use exceeds 300 kWh, the excess is billed per the TEPCO rate table"). AC is the only realistic way for one tenant to cross 300 kWh. The clause is written for August.
A third pattern absorbs everything. The contract states the kōnetsuhi as a fixed amount with no overage clause. Some operators call this 完全定額制 (kanzen teigaku-sei — fully fixed-rate) on the listing. On a hot August, the operator eats the loss.
A fourth pattern doesn't bundle at all. Each unit has its own TEPCO contract in the operator's name. The tenant pays metered usage at the end of the stay. There's no flat fee, so nothing to clawback against. The listing page calls it 実費精算 (jippi seisan — actual-cost settlement) in the fine print. The "guideline" monthly figure quoted is roughly the average August on an average unit.
Four buildings on the same Setagaya street can run all four patterns. The rent line on each looks similar. The August invoice on each looks nothing alike.
Walk the math at three usage levels under the most common pattern, the ¥15,000 ceiling with metered overage.
Light August: 180 kWh, working from the office, AC on 6 hours a day. Metered cost is ¥6,300 electricity plus ¥6,000 gas and water. Total: ¥12,300. That's below the ¥15,000 ceiling. The tenant pays ¥15,000 anyway. The operator keeps ¥2,700.
Normal August: 220 kWh, the bet case. Metered cost ¥13,700. Below the ceiling. Tenant pays ¥15,000. Operator keeps ¥1,300.
Heatwave August: 380 kWh, the eighth-floor west-facing case. Metered cost ¥20,000. Above the ceiling. Tenant pays the ¥15,000 base plus a ¥5,000 supplemental. The operator still keeps ¥1,300, the same margin as a normal month.
The flat fee only goes one way. In cool months the operator keeps the gap. In hot months the operator passes the gap to the tenant. The bundle bundles in the operator's direction.
A tenant reading "utilities included, ¥15,000/month" reasonably expects to win some months and lose others. The clause says they only ever lose.
Which pattern shows up where isn't random. It tracks the rent band of the listing.
Budget tier (under ¥200,000 a month for a studio) skews to ceiling-with-overage. The math works for the operator because the budget shopper compares on rent plus headline kōnetsuhi and rarely reads clause 14.3 before booking. The August clawback recovers margin without losing the booking.
Corporate-relocation tier (¥350,000 and up for a one-bedroom) skews to fully fixed. Corporate tenants run contracts past their company before signing. Unbounded utility clauses don't survive that review. Operators in this tier price the kōnetsuhi higher year-round and absorb hot months themselves.
Middle tier (¥200,000 to ¥350,000) is mixed. Some bundle with overage. Some itemize from day one. Almost none fully absorb. The unit is competing on per-night math against Airbnb, where electricity isn't itemized at all.
If you want to know what a specific listing does, the question to ask the operator isn't "what is the kōnetsuhi." It's: "is the kōnetsuhi 完全定額制 or は月額に上限ありますか" ("is it fully fixed-rate, or is there a monthly cap?"). One sentence in Japanese. The operator's answer takes ten seconds. Reading clause 14.3 of a draft contract takes longer.
The worst case: a booking made in March for a stay starting in late July. The tenant compares six listings on rent and headline kōnetsuhi alone. The five-month gap between booking and arrival is also the gap between signing the contract and the heatwave arriving. The clawback clause sat in the contract from day one. The tenant finds out in late August, when the supplemental invoice arrives.
The yen amounts aren't huge. ¥5,000 to ¥9,000 of supplemental utility on a ¥210,000-a-month stay is 2% to 4%. The grievance isn't the amount. The grievance is that the listing said "utilities included" and the August invoice said something different.
There's a second-order effect. The clawback also weakens the operator's reason to keep the AC working. An operator absorbing all August utility has every reason to keep the aircon working. Spec a good unit. Replace it on a 7-year cycle. Answer service calls fast. An operator who passes overage to the tenant has roughly half that reason. The unit cools poorly. The tenant runs the AC harder. The supplemental invoice grows. The tenant pays both costs.
So operators who absorb utilities tend to spec better cooling hardware. Not a coincidence. The same accounting decision drives both.
If you're booking now for any stay that overlaps July, August, or September, ask the operator three questions in writing before signing.
First: is the kōnetsuhi fully fixed (完全定額制), or is there a monthly threshold above which use gets billed at meter? If the answer is the second, ask for the threshold in kWh or yen. Then ask whether overage is billed at TEPCO's published rate or some other rate.
Second: which clause of the draft contract states the overage rule? The clause number varies. Sometimes 14, sometimes 8, sometimes 22. The operator should be able to point to it in one reply.
Third: what did the supplemental invoice look like in August 2024 or August 2025 on a comparable unit? Operators who absorb will say the question doesn't apply. Operators who clawback will give a yen range. A non-answer is also an answer.
Say your unit is on the third or sixth floor facing east or north, and the clause is ceiling-with-overage. The bet is probably fine. If the unit is on the eighth floor or higher and faces west or southwest, the bet is against you. Ask if a different unit is available, or whether the operator will cap the supplemental at a number you can write into your budget.
The kōnetsuhi flat fee is priced for an average month. August on the wrong unit isn't average. The clause that decides who pays for the gap is already in your contract. Find it before the heatwave does.
— HalfKey publishes the kōnetsuhi clause type on every unit page. Browse listings for your dates.