Underbook: Hotel Price Comparison & Tracker by Underbook

Compare hotel prices on the hotel page you are already looking at: Underbook shows whether another booking site lists the same stay for less, and whether that lower price names the same room.

Free hotel price comparison on Booking.com, Expedia, Hotels.com and many other booking sites and hotels' own websites. Prices are compared all-in where the sites report taxes and fees, and you can get a free price-drop alert by email, even after you book. Where the banner does not appear on its own, click the Underbook button in the toolbar to check that page.

Honest by design
A lower price is only useful if it is for the same room. When Underbook can match the room name, it shows both names. When it cannot, it says so in one line: the lower-priced site "doesn't name the room. Check it before you book." A price marked as members-only is shown in a note, never as the lower price. When the site you are on already has the lowest price we found, we tell you that instead of inventing a lower price.

Why bother
In our hotel price study (16 snapshots from September 22 to October 3, 2026, 6,663 hotel prices in 358 cities), 61% to 81% of hotels in each snapshot had at least one site listing the stay 5% or more below the going rate. Most of those cheaper listings did not name a matching room, which is exactly why Underbook tells you whether the room names match before you switch. The full study and its data

How it works

1. Shop for hotels as you always do.
2. On a hotel page, Underbook checks other booking sites for the same dates and party size.
3. If one is cheaper, you see the price, the site, whether the room names match (or that the cheaper listing names no room) and whether free cancellation is labelled. You always book on the site you choose.

Price-drop alerts (optional)
Enter your email in the price-drop box on the banner. Underbook checks the typical rate for those dates once a day and emails you when it drops at least 5% on two daily checks in a row. Emails about that stay only, and at most one drop alert. No account. One click stops it.

Already booked? (optional)
Right after you book on Booking.com, Expedia, Hotels.com or Agoda, Underbook can offer, once, to watch that booking, with the hotel, dates, price and free-cancellation date filled in from the confirmation page for you to check. Nothing about the booking is sent unless you type your email and press the button. Underbook checks once a day until free cancellation ends, emails you once if a listed rate is at least 5% lower on two daily checks in a row, and reminds you a week before and the day before your free cancellation ends. You can also tick "I already booked this stay" on a hotel page and type the details. Check the room before you rebook. Underbook never reads your booking number, name or payment details.

What Underbook sends, and why

• To compare prices, the extension sends the hotel name (and its town, when the page shows one), your dates, the number of adults and the site's market and currency to Underbook's price service. It does not send your identity, your browsing history or any payment details.
• Anonymous usage statistics (for example, "a comparison was shown") are sent only if you allow technical and interaction data for Underbook in Firefox: a choice in the install prompt, and later in the add-on's Permissions and data settings. They never include hotel names, dates, URLs or your email.
• Your email is stored only if you set a price watch, and only to email you about that stay. For a stay you already booked, Underbook also keeps the price you paid and your free-cancellation date, and deletes the record after check-out.
• On the booking confirmation page of those four sites, the extension reads only the hotel and its town, the dates, the number of adults, the price and its currency and the free-cancellation date, to fill in its offer. It sends them only if you set the watch, and it never reads your booking number, name or payment details.
• We never see your card and we do not sell data.

Full policy: underbook.co/privacy

How Underbook is free
When you open a booking site through Underbook and book, we may earn a commission from that site at no extra cost to you. It never changes which prices we show or their order.

No extension handy? Check any hotel on the web: underbook.co/hotel-price-checker
Help and questions: underbook.co/help