Gatwick Airport to Bath help

https://tfl.gov.uk/

This is the official guide to London regional transport. It will show you alternatives on the your, although the train appears to be the main choice.

Or you can use Google Maps (the link varies depending on where you are living.) It shows the train possibilities, complete with map.

I often suggest looking at the links shown by airport websites but the Gatwick site uses the Google service anyhow. It still might be worth a look for general terminal information.
https://www.gatwickairport.com/

Trains leave from Gatwick for Reading every hour where you change for Bath. For example if you buy the Off-Peak single to Reading, and a Super Off-Peak from there to Bath the combined price is £47.10, or round about £63 for the two with the Railcard (much cheaper than buying one single for the whole journey and other splits mght be even better). Compare this with the available Advances on the day and decide on your risk factor. Do remember you won't be able to use the Two Together card before 9:30.

. It looks like we could save close to 80 pounds by purchasing an advance ticket but so many variables i.e. plane delay, custom delay

Here is another option to price out.

1) An advance ticket for the 11am train
2) A second advance ticket for a train that leaves in the late afternoon as an insurance policy if your flight is delayed

Sometimes advance tickets are so cheap that buying two tickets is still less than the offpeak fare.

jr,

You could also travel via National Express bus on that route, which might be a bit cheaper but will take longer. I believe the bus heading for Bath has a change at LHR.

It looks like leaving Gatwick on the 10am or later service that goes directly to Reading - where you change for an express to Bath, is the cheapest. So, let's assume that you have the 2 Together Railcard.
Advance book the 10am from Gatwick to Bath comes with a price of £18.50 one way for the 2 of you - if done reasonably soon for your date.

However, pay on the day for the same train can be done as follows by splitting the ticket at Redhill (you simply stay on the train at this stop):> Gatwick to Redhill Anytime Day Single = £5.20 + Redhill to Bath Super Off Peak Single = £43 giving a total of £48.20 with the Railcard.

It appears that you have already made your flight reservations, and so what I have to say may be irrelevant. It is possible to fly into Bristol. You would have to change planes in Dublin or Amsterdam, depending on the airline. The train from Bristol to Bath is much shorter than the one from Gatwick.