Live rates from the European Central Bank, refreshed once a day. Unlike a physical unit, a currency rate is only true for a moment - so the date it's from is never hidden in a footnote here.
This page tries to fetch a fresh rate from the European Central Bank every time you visit. If that fetch can't complete - no connection, or the source is briefly unavailable - it falls back to the last rates it successfully saved, clearly marked as such, rather than showing nothing or silently using a guess. Either way, the date shown is the date the number is actually from.
These are the ECB's reference rates - the "mid-market" rate you see quoted in the news. No bank, card, or airport kiosk gives you that rate. Card networks typically add a small margin, banks add a foreign transaction fee on top (often 1-3%), and cash exchange desks - especially at airports - can sit 5-10% or more away from mid-market. The honest way to use this page: treat the number as the fair-value baseline, then compare whatever rate you're actually offered against it. The gap between the two is the real cost of the exchange, and it's the number providers are least eager to show you.
One more practical note: when a card terminal abroad offers to charge you in your home currency instead of the local one ("dynamic currency conversion"), the exchange rate buried in that convenience is almost always worse than your card's own. Paying in the local currency and letting your card convert is usually the better end of the deal.