The definition of success is different for everyone. For some it’s a lofty title and six-figure salary; for others it’s feeling like they’re making a difference. Others want a fulfilling career alongside the other important things in life: friends, family, and generally having a life outside work.

While each person has their own vision of what success looks like, the £100bn+ global consulting sector has a very set measure of success for its staff: revenues generated. Assessment of staff at consulting firms from manager grade (the middle of the consulting ladder) upwards can broadly be summed up as “bigger is better”–the more work a consultant has brought in over the course of the year, the higher the rating in their appraisal.

The problem is that judging a consultant solely on their absolute numbers doesn’t work for managers that aren’t there for part of the year, or that work part time. More often than not this ends up penalising women disproportionately, as they are still more likely than their male colleagues to take time out to care for young children or to work part time.

This issue is highlighted in a new Source Global Research and Unida report on Women in Consulting launched today, sponsored by EY, the report questioned around 300 senior managers on their experiences within the sector, including the use of revenues as a yard stick to success.

One senior manager commented: “You’re always compared with your peer group which are mostly male senior managers. They don’t work part time, but partners still compare hard figures like chargeability and revenues without taking into account that some of the women work part time, and will therefore obviously have lower figures. When you compare on those hard facts alone, you’re always going to lose out. I found it so frustrating.”

Consulting firms have made huge effort to introduce family-friendly policies to mitigate what is an inherently difficult working environment: long hours, demanding projects and extensive travel are all the norm.  The number of female partners is growing as a result, but the rate of change is still slow. One of the reasons these policies are failing to make more of an impact is because women’s careers are effectively stalled by standardised, revenue-based promotion criteria that fails to take into account their changing circumstances.

Detractors who think that women in what our report is calling the ‘pinched middle’ (where senior managers are expected to be full throttle in career terms, just when they’re becoming busier at home) simply aren’t ambitious enough, or don’t want successful careers enough are wrong. In fact, 82% of women at this stage of their career describe being promoted as “very important” to them–higher than the proportion of men saying the same thing (78%).

So what can firms do to hang onto their ambitious female senior managers? The first thing consulting firms could do is to stop auto-populating revenue targets by grade; they need to be tailored to each individual, taking into account actual days worked and the proportion of time spent delivering versus selling work. Over 80% of the women surveyed said that adjusting revenue goals would help keep them in consulting. Second, firms need to be clear about how part-time roles contribute towards promotion–at the moment the tendency is to pigeon-hole women working part time into back office, non-client facing roles that don’t contribute to their longer term aims.

For this to work, consulting firms need to be more sophisticated altogether in how they assess individuals. Rather than focusing on the revenues generated over a single year, firms should view careers as a long-term plan. As one woman we spoke to summarised: “Firms always talk about career plans, but they fail to appreciate that a lot of women’s career plans are built around family and children—and that it’s no less a plan because of it.”

Alison Huntington is a Senior Analyst at Source Global Research, the leading research and strategy firm for the global management consulting industry.