No, there is no formula. There is a list of factors the courts have to consider set out in the Matrimonial Causes Act 1973:
(a) the income, earning capacity, property and other financial resources which each of the parties to the marriage has or is likely to have in the foreseeable future, including in the case of earning capacity any increase in that capacity which it would in the opinion of the court be reasonable to expect a party to the marriage to take steps to acquire;
(b) the financial needs, obligations and responsibilities which each of the parties to the marriage has or is likely to have in the foreseeable future;
(c) the standard of living enjoyed by the family before the breakdown of the marriage;
(d) the age of each party to the marriage and the duration of the marriage;
(e) any physical or mental disability of either of the parties to the marriage;
(f) the contributions which each of the parties has made or is likely in the foreseeable future to make to the welfare of the family, including any contribution by looking after the home or caring for the family;
(g) the conduct of each of the parties, if that conduct is such that it would in the opinion of the court be inequitable to disregard it;
(h) in the case of proceedings for divorce or nullity of marriage, the value to each of the parties to the marriage of any benefit which, by reason of the dissolution or annulment of the marriage, that party will lose the chance of acquiring.
The goal is to achieve a fair split. That may mean you are entitled to 50% but it could be more or less than that.