The Mortgage Market Review (MMR) rules aim to ensure there is no return to any irresponsible lending practices of the past.
But some concerns have been raised that it could slow down the housing market, which has been springing back into life over the last year, as the industry adjusts.
Each lender will have their own interpretation of the new rules, but in general people are likely to be asked for more detail about regular outgoings such as childcare, food, household bills, loans, credit cards, toiletries, hobbies and leisure activities, to see if they can afford a home loan.
It's important for people to prepare a lot earlier, potentially six months before you apply. Start looking through your documentation and go through a budget.
Lenders will also look for any impact that future life changes could have, such as when they plan to retire and how they plan to spend their old age.
There have also been reports of some people being asked if they are planning to start a family as lenders gear up to comply with the rule changes.