About Zenrate

Why we built Zenrate

Most currency converters answer one question: what is 100 USD in JPY right now? That is useful for about ten seconds. Then real life shows up — you land in Tokyo with a stack of receipts, your company's expense system wants the rate from the day of the transaction, your accountant prefers a specific Japanese bank's published TTM rate, and the number you screenshotted from a generic converter does not match any of that.

Zenrate exists because I kept hitting that gap myself. I am Koryu, the founder of Endots LLC, and I built this tool first for my own travel and accounting workflow before turning it into a product. Every rate source, every export format, every small UI decision came from a receipt I actually had to reconcile.

The two modes, and who they are for

Zenrate has two modes, aimed at two different moments in a traveler's day.

Convert is the fast lane. You are at a counter, a menu, or a hotel front desk, and you need to know what something actually costs in your home currency. It loads instantly as a PWA, works offline once cached, and supports 160+ fiat currencies. We removed crypto mode in 2025 because it diluted the focus — if you are converting Bitcoin, you are not the user we are optimizing for.

Expenseis the slower, more careful lane. After the trip, you have a folder of receipts and a deadline to submit a report. Expense mode lets you log each transaction with the correct historical rate for your company's accounting policy, attach a receipt image, and export a file your accounting software can actually import.

Most converters stop at the first mode. Most expense apps do not care about rate accuracy. Zenrate sits in the middle on purpose.

Rate sources, and when each one matters

There is no single "correct" exchange rate. There are several public reference rates, and the right one depends on your company's policy, your country, and sometimes the specific transaction type.

Zenrate currently fetches rates from two production sources, with additional sources on the implementation roadmap. The two production sources today are the European Central Bank and Mizuho Bank.

European Central Bank (via the Frankfurter API)

The ECB publishes a daily euro foreign exchange reference rate at around 14:15 Central European Time on business days. These are the rates that end up in most European financial news and are widely used by businesses inside and outside the Eurozone for accounting translation.

Use this when your company operates in the EU, your accountant works in euros, or your policy explicitly references "ECB rate." Also a sensible default for personal travel expenses if you have no specific employer policy.

Mizuho Bank TTM, TTS, and TTB

Mizuho is one of the major Japanese megabanks, and like its peers it publishes daily Telegraphic Transfer rates on business days in Tokyo. TTM is the middle rate, TTS is what the bank sells foreign currency for, and TTB is what it buys foreign currency at.

In Japanese accounting practice, the TTM rate from a major bank (MUFG, Mizuho, or SMBC are all common choices) is what most companies reach for when translating foreign-currency transactions. There is no rule saying you must pick Mizuho over the others — Zenrate uses Mizuho as its default because Mizuho publishes its rates in a CSV format we can fetch reliably, which means less manual work for you. The numbers are within a hair of MUFG and SMBC anyway.

Use TTM when translating an expense for a Japanese company's books. Use TTS when calculating what it would cost to buy foreign currency at a bank counter. Use TTB when calculating what you would receive selling foreign currency back to a Japanese bank.

For currencies that Mizuho does not list directly, Zenrate cross-rates through USD automatically — the same approach Japanese accounting teams use manually.

Planned: U.S. Treasury Reporting Rates

The U.S. Department of the Treasury publishes foreign currency exchange rates that U.S. federal agencies use for reporting. They are updated quarterly with mid-quarter amendments when a currency moves more than ten percent.

This source is on the implementation roadmap for users who need to file U.S. tax-related foreign currency translations or whose finance teams have standardized on Treasury rates for consistency across quarters. Until it ships, U.S.-based users can pick ECB rates (close to Treasury but not identical) or import statement rates manually.

Planned: HMRC Monthly Average Rates

His Majesty's Revenue and Customs in the UK publishes monthly average exchange rates that businesses can use for VAT returns and accounting periods. These are calculated from spot rates across the month and are intended to smooth out volatility.

This source is on the implementation roadmap for UK businesses on monthly accounting cycles. Until it ships, UK users can pick ECB rates for daily granularity or compute their own monthly averages from ECB historical data.

Six rate policies, because companies do not all agree on the date

Even within one rate source, companies disagree about which day's rate to apply. Zenrate supports six policies.

1. Transaction date

Use the rate published on the day the transaction actually occurred. Most common globally. The rate engine handles holidays by falling back to the previous business day automatically.

2. Prior month end

Use the closing rate from the last business day of the previous month, applied to every transaction in the current month. Common in Japanese SMEs for stability and audit simplicity.

3. Month start

Use the rate from the first business day of the current month. Similar reasoning to prior month end, but locked at the start of the period rather than the end.

4. Prior month average

Use the arithmetic mean of all business-day rates from the previous month. Smooths out single-day spikes. Useful when the previous month had unusual volatility.

5. Prior week end

Use the rate from the last business day of the previous week. Suits weekly expense submission cycles.

6. Credit card statement rate

Use the rate the credit card network actually applied, entered manually from the statement. Required when reconciling expenses to a corporate card statement, because any other rate source will be off by the card network's margin.

Receipts that hold up to an audit

A converted number on a spreadsheet is not an audit trail. A receipt photo on your phone with no timestamp is not one either. When you save a receipt in Zenrate, the system records the original image, the rate source, the rate policy, and the exact rate value used at the time of entry, all with a server-side timestamp. If your accountant later asks where a number came from, the answer is on the page.

Export formats that match real accounting software

Zenrate exports directly to the formats used by freee and MoneyForward Cloud (the two most common cloud accounting platforms in Japan), QuickBooks (US), and Xero (UK, AU, NZ, and increasingly global). Each export uses the column headers and data formats those tools expect on import.

What Zenrate does not do, and why

No crypto. Cryptocurrency conversion has different volatility patterns, different rate sources, and a different user base. Trying to serve both was making both worse. We removed crypto mode in 2025.

No real-time trading rates. The rates here are reference rates suitable for accounting and traveler use. If you are trading FX professionally, you need a different tool.

No ads inside the converter itself. The Convert and Expense screens stay clean.

Who is behind this

Zenrate is built and operated by Endots LLC, a small independent software company. I am Koryu, the founder and the person who writes the code, answers support email, and decides which features ship. There is no growth team, no AI-generated content farm, and no investor pressure to add features that do not help the actual user.

You can reach me directly at the contact link in the footer. If you are a tax professional, accountant, or finance team lead and you spot something Zenrate gets wrong about your jurisdiction's conventions, please tell me — I would rather fix it than keep shipping a tool that misleads people.

Roadmap

The current focus, in order:

1. Tightening the Expense mode workflow based on the first few months of real usage
2. Implementing U.S. Treasury and HMRC rate-source fetchers to bring the rate engine to four production sources, matching what the rate-source registry already supports
3. Direct integration with freee and MoneyForward (instead of CSV import)
4. An "Exchange Finder" map showing crowd-sourced rates at physical exchange counters in major travel hubs, starting with Narita, Haneda, and Kansai airports
5. Native iOS and Android apps once the web version is fully stable

If any of this is useful to you, the tool itself is free at the homepage. No signup needed for Convert mode. Expense mode requires a free account so we can store receipts and rate history across devices.

— Koryu, Endots LLC