The extra cash on top of the previous budget of £14.8bn was confirmed in an annual update to parliament today.
Crossrail is getting £300m directly and a further £290m is also being handed to Network Rail to complete its upgrades to the existing network.
A spokesperson for Crossrail said: “The construction of the Elizabeth line is one of the most complex and challenging infrastructure projects ever undertaken in the UK.
“Construction is now in its final stages with a huge effort underway to complete and commission the new railway.
“A number of factors have meant that additional investment is needed by both Crossrail Limited and Network Rail during this final stage of the programme covering both the new build central section and upgrades to the existing railway.
“These cost increases are disappointing but additional funding is critical to the delivery of this vital project.
“£300m will be made available to Crossrail Limited for its remaining programme of works in the central section.
“Both Crossrail Limited and Network Rail remain focused on managing costs through to project completion.”
The Enquirer has reported repeatedly on the cost pressures facing the project at the M&E fit out stage.
Crossrail’s official line has always been that the scheme is “on time and on budget”.
One site source said: “Everyone on the ground knew it wouldn’t hit the budget.
“You always get cost over-runs at the M&E fit out stage on a job like this.”
Crossrail Chief Executive Andrew Wolstenholme stepped down as project leader five months ago.