If we talking purely financially, then I honestly have no idea. I can see no earthly way in which the 'Olympian boost' to London's economy can exceed the cost of staging the Games.
It depends on how you use the site afterwards.
If you use the Olympics to try and regenerate an area then you can get more out of it.
This area need improved transport links and regeneration , and hopefully the site wil get used again, the plan is to have a rugby & football club use the stadium and it is now down for the 2017 World Athletic chanpionship already.
It might be the bost the area needs like the O2 does for north greenwich.
It alos brings feeling of fun and excitmeent ot he city, I can tel you that London was buzzing my way during the games, and it is still with the paralympics, i was lucky ot be in a packed stadium of about 70,000 on the first day of atheltics !! brilliant atmosphere.
The Athletes in that host area later have the best of and an up to date place to obtain and the children that have watched do also have the best ,
as in other cities where the Olympics that they hosted was in need as to a refurbishment this later brought income to the areas that were not going to get
One of the reasons that a city does it is to show to the world they are capable of holding world class events which in turn means they are more likely to get other world class events e.g. Rio got the World Cup.
I know that doesn't apply to London an I actually can't figure why they did when they know the direct and indirect benefits simply do not add up to the ongoing benefit.
Facilities and infrastructure are sometimes required in a city and the Olympics pushes those e.g; Barcelona.
the olympics are pretty much a big deal even though it may cost millions to prepare for they want to be the host cause with the olympics you get more tourists with more tourists means more money for the businesses and city itself
The city makes tons of money from the tourists as well as the publicity the city gets is priceless.
Tourism
It boooooooms the economy with all of the visitors stopping by. It's a good thing.
they make millions off tourists and what not
It costs so much money and that money could be used for other stuff.
