One of the most contentious parts of Brexit has been the discussion surrounding the so-called 'divorce bill'.
It is a complicated area that will be a key feature in discussion between EU and British negotiators over the coming months.
Since talks began a lot of numbers have been thrown around, ranging from as little as nothing to as much as €100bn.
But with no precedent in a nation leaving the EU, the final figure will have to be hammered out at the negotiating table in Brussels.
Why does Britain owe money?
As a member of the EU Britain has paid large sums of money towards projects such as road, rail and investment.
Some of the money stems from a pledge made by David Cameron when he was prime minister, committing to the EU budget until 2020.
The UK had also agreed to pay for other programmes between 2019 and 2025.
On top of this, Brussels wants Britain to ensure that pension costs towards officials and MEPs are covered, as well as other similar liabilities.
Howe much does the EU want?
The Brexit negotiating team are yet to confirm the number that they want.
But ardent Brexiteers, such as the Conservative backbencher Jacob Rees-Mogg, have suggested that Britain "owes nothing" to the EU.
The most recent figure to enter the headlines was €40bn, which was denied by Down Street.
But that figure looks the most likely outcome once talks have concluded, it isn't the €60-80bn that some EU nations have pushed towards, and isn't the zero figure that the like of Rees-Mogg have called for either.
When will an agreement be met?
However, time is not on the side of British officials, Article 50 was triggered more than five months ago. That leaves only around a year-and-a half until the country is due to leave the EU.
On the other side, Brussels has made it clear that until "sufficient progress" is made on the divorce settlement, the next stages of the negotiations may have to be put on hold.
This "progress" also applies to citizens' rights and Northern Ireland, meaning that the negotiations are set to enter their toughest period yet.