Regulations come into force in April affecting companies employing at least 250 workers aimed at revealing differences between the pay of men and women.
Latest figures from the Office for National Statistics showed that the gender pay gap for full-time workers was 9.4%, rising to 18.1% for all employees.
The conciliation service Acas said the new reporting rule will apply to 8,000 businesses, voluntary and charitable organisations.
Chief executive Anne Sharp said: “The new requirement provides a great opportunity for organisations to look at the issue in depth and to consider whether they can do more to develop their talented women and secure the benefits of greater gender diversity at all levels.
“The UK has made progress in reducing the gender pay gap but we still have lots to do - tackling the issue is in the interests of individuals, organisations and the economy as a whole.
“Our new guidance on gender pay reporting provides businesses with practical advice on how to carry out the calculations and on family-friendly working to reduce the gap.”
Equalities Minister Caroline Dinenage said: “No-one should ever be held back just because of their gender. We now have the lowest gender pay gap on record, but we still have to push further.
“Shining a light on the gaps is absolutely key to achieving equality in the workplace.”