Difference of latest dates.

[DOCKPORT]

I'm a bit puzzled. My app follows UTC time. I know this API doesn't follow UTC time, but I got this recently: for https://api.frankfurter.dev/v2/rates?base=USD I see the dates as 2026-07-03, but for https://api.frankfurter.dev/v2/rates?base=USD&from=2026-07-01 I see rates showing 2026-07-04... Which is it? which is the latest one?

[lineoffligbot]

Good catch, and sorry for the confusion. Two things are going on here, one of which was a real bug on our side.

First, the API clock is UTC. An open-ended query ("latest", or from= without to=) is anchored on the current UTC date. What is not UTC-aligned is the data itself: the date on each record is the observation date the source published, in its own local business calendar. With 80+ sources across timezones, a latest snapshot legitimately mixes dates. A few central banks even publish their official rate dated the next day (for example Georgia and Kyrgyzstan), so rates dated 2026-07-04 existed in the database on Friday afternoon.

Second, the inconsistency you saw was a CDN caching bug. Those forward-dated rows only enter scope once the UTC date rolls over to 2026-07-04, but our cache was only purged when new data arrived, not at midnight. Your ?base=USD URL served a response cached before midnight (all 2026-07-03), while your ?from=2026-07-01 URL was a cache miss computed fresh after midnight, which already included the 2026-07-04 rows. Fixed in #542: open-ended responses now expire at UTC midnight, so the two can no longer disagree.

As for "which is the latest": trust the date field on each record, not the moment you queried. The latest endpoint returns the most recent observation per currency pair, and those dates can differ across pairs by design. If you need a consistent daily series in UTC, query explicit dates and key your data off each record's date.

[DOCKPORT]

Glad to have contributed.

[DOCKPORT]

This might be a bug as well:
Link: https://api.frankfurter.dev/v2/rates?base=USD , example: {"date":"2026-07-08","base":"USD","quote":"CHF","rate":0.80635}
Link: https://api.frankfurter.dev/v2/rates?base=USD&from=2026-07-07 , example: {"date":"2026-07-08","base":"USD","quote":"CHF","rate":0.80637}

Notice the rate difference

[lineoffligbot]

We have opened pull request #544 to cap the WeightedAverage reference date at Date.today. This ensures todays rates maintain full weight (age 0) even when tomorrows rates are present in the snapshot, resolving the discrepancy between latest and range queries.

[DOCKPORT]

What is it weighted by? I understand using an average of multiple sources, but the weight, what is it for? trading volume? (usually weighted average is trading volume, but I dont think we have trading volume here)

Also, regarding the UTC day shift, how long does it takes for the data to sync after midnight UTC? for crypto apis its instant, but I guess here we have a slight delay? maybe a few minutes?