بسم الله الرحمن الرحيم
If you mean by calculating zakah as per total assets that whatsoever you own such as residential house, house belongings etc and you pay zakah of all these things then be informed that there is no zakah on these things. Zakah is wajib only on gold, silver, money, business goods when it reaches up to the value of nisab. In the question mentioned above when both of you are sahib-e-nisab then separate zakah will be wajib on both of you. Whatsoever you (husband) own should calculate its fortieth part on the date of zakah and keep it separate while your wife should also calculate whatever she owns and keep its fortieth part separate. Then at the time of paying zakah you are free either combine both the amounts or pay your zakah separately; both the methods are correct. If the income of both of you is combined then pay the fortieth part of the total income. For example, if one thousand becomes the zakah of both of you then keep that one thousand separate so that you could give it to the needy ones. Zakah will also be paid if the husband paid seven hundred rupees to some needy person and the wife paid the remaining three hundred to someone.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.