Tesco now projects operating profit over the full year of up to $2.9 billion.
It blamed uncertainty over how the cost-of-living crisis will hurt spending by shoppers.
British consumer confidence sank to a record low last month largely due to higher inflation
That was also before the government's mini-budget hit the mortgage market, and led to warnings of a sharp drop in house prices.
Wages have also not kept pace with inflation - which was at 9.9% in August.
Tesco noted consumers were buying less per shopping trip, and trading down to cheaper own-label products.
The retailer reported first-half retail adjusted operating profit of about $1.4 billion.
That was down 10% from last year, and just below analysts' average forecast,
First-half group sales rose 3.1% to $32 billion.
Tesco's shares have fallen more than a quarter so far this year,
Though monthly industry data has shown the firm outperforming its biggest rivals - Sainsbury's, Asda and Morrisons - on a sales value basis.
STORY: Full-year profit will come in at the lower end of previous guidance for Tesco.
