Flight Price Tracking Apps Compared: Slipfare vs. Google Flights vs. Hopper vs. AwardFares

There are dozens of tools that claim to track flight prices, but they don't all solve the same problem. Some help you find the cheapest time to book. Others watch a fare after you've already bought it. A few focus on award flights. Understanding which tool does what — and what it can't do — saves you from relying on the wrong one. Here's an honest breakdown of four popular options.

The fundamental split: pre-booking vs. post-booking

Before comparing individual tools, it helps to understand the two main categories of flight price tracking:

• Pre-booking tools help you decide when to buy. They track fares on routes you haven't booked yet and alert you when prices look good. Google Flights and Hopper fall squarely in this category.
• Post-booking tools monitor fares on flights you've already purchased. The goal is to catch a price drop so you can cancel and rebook at the lower price, pocketing the difference as a credit or refund. Slipfare is built specifically for this.

These are fundamentally different use cases. A tool that's great for finding deals before you book may be useless for monitoring a fare after you've committed. For more on the various approaches, see our guide to tracking flight prices after booking.

Google Flights

Google Flights is the gold standard for pre-booking research. Its fare calendar, flexible date search, and route explorer are unmatched for finding cheap flights. The "track prices" toggle lets you set alerts on specific routes and dates, and the price history graph gives you a rough sense of whether fares are high or low relative to the norm. It's free, fast, and covers virtually every airline. We go deeper in our full Google Flights guide.

The big limitation: Google Flights has no concept of "your booked flight." It tracks routes, not reservations. It won't compare the current price to what you actually paid, and it won't tell you whether a drop is large enough to justify rebooking. Its price alerts tend to be inconsistent, it only tracks cash fares (no award flights booked with miles), and it doesn't cover Southwest. Cost: Free.

Hopper

Hopper's main value is its price prediction engine. It analyzes historical data to tell you whether a fare is likely to rise or fall, giving you a "buy now" or "wait" recommendation. For flexible travelers who want data-driven guidance on when to pull the trigger, this is genuinely useful. Hopper also sells "Price Freeze" and "Cancel for Any Reason" add-on products that provide a form of price protection at booking time.

However, Hopper is designed entirely around the pre-booking decision. Once you've bought your ticket, the app doesn't monitor your booked fare for drops. Price Freeze locks a fare for a limited window before you buy — it's not the same as post-booking monitoring. Hopper also only covers cash fares, has no award flight tracking, and acts as an OTA for bookings made through the app, which can complicate changes and cancellations. Cost: Free for predictions and alerts. Price Freeze and insurance add-ons run $2–$60 depending on the fare.

AwardFares

AwardFares fills a niche that most other tools ignore: searching award flight availability across multiple loyalty programs. If you have a stash of miles and want to find the best redemptions across airlines like United, SAS, or Air Canada, AwardFares aggregates availability into a single dashboard. It's particularly useful for finding premium cabin award space, which is notoriously hard to track. For more on how award flights work, see our beginner's guide to award flights.

The limitation: AwardFares is a pre-booking search tool. It helps you find open award seats, but it doesn't monitor the price of an award flight you've already booked. If you book a United award at 45,000 miles and the price later drops to 30,000, AwardFares won't alert you. It also doesn't track cash fares at all. Cost: Limited free tier. Paid plans start around $7.99/month.

Slipfare

Slipfare is purpose-built for the post-booking problem. Forward your booking confirmation email, and it automatically monitors the fare on that specific flight. If the price drops below what you paid — in cash or miles — you get an alert. Unlike the other tools on this list, Slipfare tracks both cash fares and award flights. If you booked a United award at 40,000 miles per person, it monitors the current award price and alerts you when it drops. This is a gap that no combination of Google Flights and AwardFares covers. For United flyers, our guide to tracking United award flights explains how this works.

Slipfare is not a fare search engine — it won't help you find the cheapest flight to book in the first place. That's what Google Flights and Hopper are for. It also doesn't handle the rebooking process; it tells you when a drop happens, and you handle the cancellation with the airline. Cost: Free tier available. Paid plans for higher monitoring frequency and more tracked flights.

Which tool should you use?

The honest answer: it depends on where you are in the booking process, and most travelers benefit from using more than one.

• Before you book (cash) — Use Google Flights for research and alerts. Hopper is a useful second opinion on timing.
• Before you book (miles) — Use AwardFares to search award availability across programs.
• After you book (cash or miles) — Use Slipfare to monitor your specific fare and get alerted to drops.

The tools complement each other because they solve different problems at different stages. Google Flights helps you find and buy. Slipfare helps you save after you've bought. Using a pre-booking tool for post-booking monitoring — or vice versa — is like using a hammer as a screwdriver. It kind of works, but there's a better option.

The bottom line

No single tool does everything. Google Flights is the best free fare search engine. Hopper adds prediction intelligence for timing your purchase. AwardFares is unmatched for finding award availability. And Slipfare is the only tool specifically designed to watch the fare on a flight you've already booked — in both cash and miles — and tell you when it drops. The smartest travelers use the right tool for each stage of the process, and that usually means at least two from this list.