The main parts of the bill are unpaid budget appropriations (basically the EU’s credit card); unused national allocations of investment spending, which Britain approved for the 2014-20 period; and the cost of the pension promises made to EU officials. The obligations are partly onset by flows of money back to Britain from its share of assets, budget receipts and the payment of the UK rebate.
In my answer below, I will detail some of the major parts of the Brexit bill.
This is mainly added from EU spending on projects that are approved and paid over a period of several years.
Reste à liquider ("yet to be paid")
Outstanding spending allocations
The Commission’s argument is that the UK jointly approved around €143 billion of investment spending that is legally binding on the EU but will only be paid once Britain has left. In EU law, these are legal commitments that become budget commitments once money is reserved to pay for them in the EU’s annual budget round. The pledges are in addition to the commitments already in the RAL, and the Commission wants Britain to honour its share. It is by far the most contentious part of the exit bill.
Pension promises to EU officials
This costs the UK €63.8 billion and is retirement benefits for EU officials. The UK would have to pay all UK nationals working within the EU institutions which would cost €80 million this year.
However, the EU Commission wants the UK to pay pensions for all EU officials, not just British nationals, since they all worked for the EU when the UK was a member. According to the EU consolidated accounts, it will cost up to a full €63.8 billion.
Other legal obligations
The Commission will seek to secure Britain’s share of funding for those commitments that are seen as legally binding, either because they are in multi-annual allocations, or arise from contracts that have already been signed.
- Connecting Europe Facility (CEF) - EU liability €10.1 billion
- Copernicus and Galileo programmes - EU liability €3.1 billion
- Miscellaneous - EU liability €3.4 billion
- European Fund for Strategic Investments (EFSI) - EU liability €16 billion
- Guarantees and provisions: €23.1 billion
- Loans: €56.1 billion
Overview of the Brexit bill calculations
(page 10; from the same document linked above)