Sales at Primark, with a store in Norwich, are set to be hit by £1.1billion in the six months to February 27, according to its owner Associated British Foods.
Bosses added they expected to lose further sales of £480m from store closures because of Covid in the second half of its financial year - March to August.
However, they said they expected the period after reopening to be "very cash generative" with £150m of sales of spring and summer clothes left over from last year.
Primark expects to have its 153 stores in England reopen on April 12, based on current guidelines.
The retailer opened a massive new superstore with a nail bar in Norwich's Haymarket just before Christmas 2019.
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