Female staff are anticipating to receive around £16,240, compared to £32,800 for men, according to recruitment firm Astbury Marsden.
The gap extends to senior levels, with female directors and other executives believing their bonus will average £25,800, almost half the £50,300 expected by men.
Adam Jackson, managing director at Astbury Marsden, said: "The City has made significant steps in combating gender equality but more can still be done to ensure that at all levels both genders are treated equally.
"The reality is that the sectors where there is a high reward culture are still male dominated with women often making up a larger proportion of the non-commission earning side of businesses such as HR or marketing.
"Trading floors for example, have a reputation for being largely a male environment and many women can be put off from applying to these types of roles.
"Some City firms have trouble attracting and retaining enough women as a result of this."