1. Make a plan of where you want to go and when.
2. Count the number of travel days you need and which pass would fit.
3. Check which reservations you would need when using a pass, how much they would cost and whether they are still available.
4. Look up prices for normal tickets.
5. Compare prices of pass + reservation against normal tickets.

Thank you very much, my idea is this: I want to go to Paris for the day and another day to Brussels also for the day. Can you buy the pass for 2 days? Should I use it on consecutive days or can it be on different days?

Ordinary tickets for London - Paris starts at £78 return, or even £58 return during a sale. The same for London - Brussels.

With the pass, you will have to pay an extra fee of about €30 for each train (€60 return) on top of the cost of the pass.

So have a look for the prices for a regular ticket at the dates you want to go. It’s almost certainly cheaper to buy a ticket, and not get a pass.

Thank you very much for your answers, I am understanding the subject a little better, I will follow your advice  =)

Hopefully you’re not travelling during Easter as trains are very expensive or sold out.

I’d also buy regular tickets on eurostar.com ASAP.

Keep that these journeys are 2h-2h30 so you’ll likely take the first train of the day if you’re really planning a day trip. Maybe a round-trip London - Paris - Brussels - London in 2-3 days would end out cheaper...

And it’ll be hard to get a return ticket for less than 170€ so a 4-day Global Eurail pass might be worth it… 250€ + 4 x 30€ reservation (if available)

Check for your dates if passholder fares are available and if regular tickets are cheaper or more expensive in the end…

https://www.b-europe.com/EN/Booking/Pass#TravelWish