The details are contained in an official analysis of the budget by the Department for Social Development (DSD).
The analysis suggests the average loss per household will be £918 per year.
Tax credits are effectively a means-tested benefit paid to people on lower incomes.
They are paid to two main groups: unemployed people with children and low paid working people who may or may not have children.
The changes to tax credits in the July budget included lowering the threshold at which payments start to reduce.
Currently tax credits payments start to reduce, or taper, once a family income reaches £6,420.
From April 2016 the threshold at which payments taper will be £3,850.
There are currently 109,000 claimants in Northern Ireland who are earning above the £6,420 threshold and have a 'tapered' tax credit award.
Once the threshold is reduced to £3,850, these claimants will have their tax credit award tapered further.
An additional 12,000 claimants will also become subject to the taper once the threshold is reduced to £3,850.
The DSD analysis also looks at other welfare changes announced in the budget, including the freeze in most working age benefits up to 2020.
Using an assumption that welfare reforms will ultimately be introduced in Northern Ireland, it estimates that the July budget will take £206m off the welfare bill in 2016/17, rising to £361m in 2019/20.
The DSD analysis does not factor in the impact of the National Living Wage or increased personal tax thresholds on household budgets.

The Stags have an option of signing a permanent deal with the 22-year-old striker.
Coulthirst, a graduate of Tottenham's academy, made just one first-team appearance while at White Hart Lane.
The striker also had loan spells with Leyton Orient, Torquay, Southend, York and Wigan.
Coulthirst will join his former team-mate Hayden White at Field Mill, after he was signed on loan from Posh a week ago.
Find all the latest football transfers on our dedicated page or visit our Premier League tracker here.

Jannette Black, head of Springhill and Auchenback Primary School in Barrhead, East Renfrewshire, was seen at a minor injuries unit on Wednesday.
East Renfrewshire Council confirmed that the incident had taken place and said an investigation into the circumstances was ongoing.
Police Scotland said the incident had not been reported to them.
A council spokesman said: "We can confirm that an incident took place at the school [on Wednesday].
"No serious injuries were sustained and the member of staff involved did not require hospital treatment, however, did attend a local minor injuries unit as a precaution.
"Incidents of this nature are extremely rare in our schools and we have a zero tolerance approach to violence at work."
The local authority rejected claims that the incident was the latest one linking the school with anti-social behaviour or a lack of action by the council's education department.
A statement said: "Any incident relating to violence which is reported to us is investigated thoroughly and the appropriate action taken.
"We do not accept the claims that have been made about the management of either our schools or the education department.
"In fact, a recent Education Scotland report on this school highlights a number of areas of improvement which have been achieved under the current management."
More than 120,000 households in Northern Ireland will have their tax credit payments reduced as a result of the July budget.
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League Two side Mansfield Town have signed Peterborough United forward Shaquile Coulthirst on loan until the end of the season.
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A primary school head teacher was taken to hospital following an attack by a pupil.