JPY to THB

Reference notes for JPY/THB

When you typically see JPY/THB

The two scenarios where this pair shows up at scale are Japanese leisure travel to Thailand and Japanese individuals on long stays — language students in Chiang Mai, retirees on Non-Immigrant O visas in Phuket, programmers on month-long workations in Bangkok. The travel case dominates by volume: a one-week trip with hotel, meals, and a few cabs generates a dozen receipts that need to be reconciled at TTM if the trip was a business trip, or simply tracked for personal budgeting otherwise. The longer-stay case is smaller in number but heavier per record. Rent in Bangkok or Phuket is typically paid in THB cash or via Thai bank transfer; the JPY equivalent on the date paid is what the individual eventually files on their Japanese tax return if they remain a Japanese tax resident. A third, narrower scenario is Japanese SMEs paying Thai contractors — design studios in Bangkok working for Tokyo agencies, factory-floor consultants commuting between Yokohama and Ayutthaya industrial estates. These payments are usually invoiced in THB and recorded against a Mizuho TTM rate on the transfer date.

How JPY/THB behaves in accounting

Mizuho publishes daily TTM, TTS, and TTB rates for THB directly on Tokyo business days. No cross-rate construction is needed. The TTM rate is what most Japanese SMEs use for translating Thailand-trip expense reports; TTS is the rate the bank applies when converting JPY into THB at a counter; TTB is what the bank gives when the traveler returns and converts leftover THB back. THB is moderately volatile against JPY. Daily moves of 0.5–1.5% are routine, and policy shifts at the Bank of Thailand can produce sharper one-day jumps. For high-volume monthly travel, the prior-month-average policy smooths these spikes; for single-trip travelers, transaction-date TTM is the conventional choice. Thailand observes more public holidays than Japan does, and on those days no fresh THB rate is published in Tokyo either. The rate-policy module falls back to the previous business day, which usually matches what Japanese auditors expect.

Common conversion mistakes for JPY/THB

First mistake: confusing TTS and TTB direction. When the traveler buys THB cash before the trip, the bank applies TTS (yen-to-foreign sale). When they convert leftover THB back to JPY, the bank applies TTB (yen-to-foreign buy). Receipts often only show the resulting THB amount, leaving the user to back out which rate type was applied; if the company's policy requires TTM but the receipt was at TTS, there is a 1–2% gap that needs documenting. Second mistake: trusting airport-counter rate signs as the basis for an accounting entry. Suvarnabhumi and Don Mueang counters quote rates 3–5% off interbank; those are transaction rates, not reference rates. The reference rate to record is Mizuho TTM (or whichever the policy specifies), and any difference becomes a separate FX loss line. Third mistake: treating a TrueMoney or Wise topup as a JPY-to-THB conversion at the moment of topup, when in fact the wallet held the balance in JPY internally and converted only on the actual purchase. Each merchant-level transaction should be its own line if the company's policy is transaction-date.

What Zenrate stores for JPY/THB

For live conversion on this page, the rate is fetched from exchangerate-api.com (USD-base, cross-rated to JPY/THB) and cached in the user's browser for twelve hours. For Expense mode entries dated in the past, the Mizuho fetcher in `packages/core/src/rate-sources/mizuho.ts` first checks the project's `bank_ttm_rates` database (populated by a server-side ingestion job) and falls back to a Supabase Edge Function call if the date is not yet cached. ECB rates for JPY/THB are also retrievable on any date the Frankfurter API has data for. All six rate policies in `rate-policy.ts` work for this pair: transaction date, prior month end, month start, prior month average (which iterates business days through the fetcher), prior week end, and credit-card statement (manual entry, no automatic lookup). Weekend transactions fall back to the prior business day automatically.

These notes describe the rate sources actually implemented in @zenrate/core/rate-sources at the time of publication. Behavior may evolve; the source code is the ground truth.