Is that all you have?

It might very well be enough…I’m bad at estimating how much you’ll need. But it’s good to have more cushion money.

Granted, the United Kingdom will probably be the most expensive of the 4 countries you mentioned (UK, Germany, Netherlands, Czech Republic), and London is the most expensive place in Britain. But the others aren’t very cheap either. Czech will be comparatively cheaper than the other 3, but it’s no longer the cheap destination it once was.

To help you figure out how much money you’ll need, try and figure out the two basics: lodging and transportation.

For lodging, try doing some online research, and look at various hostel prices in the four cities you mentioned. Hopefully this can help you figure out a general price-per-night that you will be paying for lodging. Assuming that you’ll pay, say, a nice 25 USD per night for 3 weeks, that amounts to 500 USD (315 GBP) over the course of 20 days.

For transportation, it helps to know what your exact itinerary is, and if you’ll be getting around by train? by plane? will you by a Eurail pass? And if so, remember that there’s still supplemental fees on some routes. Without a eurail pass, take a look at individual train tickets, and how much they cost.

Have you even figured out an itinerary yet? It seems you just looked at a map, and picked four capital cities…I hate when people do that. Honestly, it’s just the lazy thing to do, and I mean that as constructive criticism. Try doing some research on additional places to visit, that are on-the-way. 21 days divided by 4 cities…even if you add commute days, you can still squeeze in a little more to see, especially since you chose a relatively compact grouping of countries. You can add, maybe, a bit of Belgium (Brussels + Liege or Brussels + Bruges), which would be perfect to break up the commute from London to Amsterdam (just take the Eurostar train from London straight to Brussels). People often overlook Belgium and plan to commute through the country without stopping there. You can perhaps also add Germany’s Rhine Valley and the city of Cologne (great way to break up the long commute from Amsterdam to Berlin). But don’t try to do too much in 3 weeks. 2-3 full days each in Amsterdam, Berlin, or Prague should be fine (and 2-4 days on London), leaving you with adequate time to add places in-between. A lot of people plan, like, entire weeks in large cities, and get bored on their 3rd day there. An additional option, I didn’t mention, would be to take a day-trip or overnight trip from London to somewhere in southern England.

Honestly, I don’t think 500-600 GBP (roughly 800-950 USD or 1000-1200 Singapore Dollars) will be enough, but you probably won’t need that much more.

So, try looking up Eurail passes, and hostels, and figure the basic costs. After that, of course, you’ll also need to eat, buy a couple souvenirs, and perhaps do laundry.