JOHANNESBURG (Reuters) -AngloGold Ashanti's first-half earnings slumped 18% from a year earlier despite increased output, with inflation taking a toll of profit and the miner warning that costs are approaching the top end of its annual forecast range.

The South Africa-based gold miner's first-half production rose by 3% year on year to 1.233 million ounces, putting the miner on track to meet its 2022 output guidance of between 2.55 and 2.8 million ounces.

But headline earnings per share, the main profit measure in South Africa, came in at 71 U.S. cents, down 18% from a year earlier. Total cash costs were up 6% at $1,068 an ounce as inflation accelerated.

We are pleased with what we were able to do, CEO Alberto Calderon told reporters, adding that most of its rivals have had serious issues with costs.

Calderon said the miner can achieve the necessary reduction in second-half cash costs to remain within the company's cash cost guidance of $925 to $1015 per ounce for the year.

The world's biggest gold miner, Newmont Corp, last week raised its annual costs forecast and warned that inflationary pressures would persist into next year.

AngloGold Ashanti, which mines in Argentina, Australia, Brazil, Democratic Republic of Congo, Ghana, Guinea and Tanzania, produced 1.233 million ounces of gold in the first half, with second-quarter output up 10% from the first quarter owing to higher grades.

Adjusted net debt fell 13% year on year to $740 million while free cash flow came in at $471 million, compared with a $25 million outflow in the first half of last year, lifted by cash distributions from its Kibali mine in Congo, a joint venture operated by Barrick Gold Corp.

(Reporting by Helen ReidEditing by Sherry Jacob-Phillips and David Goodman)