Google flights[1] kind of does this. If you put in an itinerary, add whatever other constraints you have (e.g. airline, flight times, fare class), and then click the calendar and wait a second, it'll eventually populate with prices under each day for changing the itinerary to that day. The cheapest day is colored in green so it jumps out.
It's not perfect, the calendar view shows two months at a time, and at times it's easier to use as starting point, but it's definitely better than clicking through 100 itineraries on an airlines slow site.
Whenever I talk to my friends from the States I get the feeling no one compares flight prices. Most of them book with 'their' fav airline of choice without comparing different options.
It depends a lot on how often you fly - I prefer Skyteam partners (ie, Delta in the US) whenever I can because I fly often enough to have award status with them, meaning lounge access, priority support, upgrades in-flight, etc... I'm sure I pay them more raw dollars than I would if I booked my trips on the absolute cheapest airline in all cases, but the perks make all the difference between the flight being a chore or a moderately pleasant experience.
I have plenty of friends, though, who don't fly as often as I do and can therefore chase the cheapest fare. It doesn't matter to them if they get a flight with an airline they don't have status with, or an airline with no special perks at all, because they're not on the road often enough to qualify for those things in the first place. Raw price wins.
Travel is one of the few industries where brand loyalty still has some tangible perks (albeit decreasing every time airlines revamp their rewards programs), so especially within the US where pretty much all of the airlines fly to pretty much all of the major airports, its an approach worth considering.
A lot of credit card deals lock you into particular airlines. Either through a card branded with that actual airline, or companies like AmEx making you choose exactly one to reap benefits with.
Take a look at https://www.skyscanner.com. They have a "cheapest month" feature. All you have to do is choose your destination.
To see it, choose your flight then in the date pop-up choose Whole Month -> Cheapest Month.
I believe they also have the inverse where you can choose a month and a departure city and they'll give you destinations by price. I couldn't find it quickly though but I think they have it.
I sometimes do the opposite for this: put my destination as my starting point, and use that to figure out which city is the best for me to fly out of.
I live near a border, and can arrange my life around a few other cities if the savings are worth it (e.g. visit family or see another city a few hours from me)
Let’s you set travel ranges, multiple destination options, geographic areas and more. Shows you the cheapest options within the range of parameters you set. My absolute favorite vacation planner.
Kiwi.com is actually really good at this. You can select flexible departure and return date, flexible departure location (eg. list of airports or simply a radius around your home) or even find the cheapest dates if you wanna stay for 3-5 nights. The features of search are best I have ever seen.
I recently moved out of state and want to fly back from time to time. I don't have any particular dates I care to fly on. I just want the most affordable option and I'll plan everything else around that.
Agree, this would be super useful! Have you tried Skyscanner's whole month feature? I believe they allow you to search for the cheapest tickets within a month and (if I remember right?) even within the year.
Recently discovered that Google flights not only has a matrix when you're choosing dates, but also has an even better one after you've already chosen dates to view the price differences for +/- 5 days on both the departure and arrival.
Just click on "Date Grid" after you search for your query and it will give you a matrix. I can't believe I just found this!
I want to put a date range and get the cheapest plane tickets.
Big range, I want to find the cheapest time of the year to fly and plan my vacation.
Nobody lets you do this.