Headline earnings per share rose 211% to 775c, net debt was reduced 58% to R580 million and the company declared an interim dividend of 110c.
Harmony said revenue was up 39% compared with the previous corresponding period, mainly thanks to a "stellar" performance from its South Africa underground operations, supported by a 31% increase in the gold price received to R896,587/kg, plus the addition of the new assets.
However Harmony said total production costs rose 30%, driven by new costs from the acquisitions, increased labour costs, higher royalties owing to increased revenues and COVID-19-related expenses.
The company said group all-in sustaining costs were therefore 18% higher for H1FY21, at R715,827/kg compared with R605,911kg a year earlier.
Production profit rose 65% compared with the previous corresponding period to R6.8 billion, gold production increased 8% to 21,411kg and underground recovered grade rose 5% to 5.58g/t.
CEO Peter Steenkamp said Harmony was "no longer a marginal gold producer but an emerging market mining specialist".
"The exceptional performance achieved during H1FY21 substantiates the growth strategy that we set out to pursue at the beginning of 2016," he said.
"These effective business practices have allowed us to create a robust yet flexible balance sheet, with a war chest of available cash and facilities to deploy in both opportune or uncertain times."
"As we move into the next phase of our growth plans, we will continue to service our communities, stakeholders and employees by doing what we know best - mining gold," he said.
Harmony had forecast net profit would be up 325-339% for the period, when it provided a trading statement update on Friday, in line with JSE listing requirements.
Other South Africa precious metals producers have tipped and reported similar bumper earnings thanks to the surge in commodity prices and weaker rand.
Harmony reiterated its commitment to a safer workplace, having reported six fatalities during the six-month period. It has since reported three fatalities in the first five weeks of 2021.
"It is simply not acceptable and will never be acceptable," Steenkamp said of the fatalities.
The company had also lost 40 employees to the COVID-19 pandemic.
"As at 19 February 2021, Harmony had 94 active COVID-19 cases, representing only 0.2% of our workforce," Steenkamp said.
The company has committed along with other miners to assist with the government's vaccine roll-out as the country battles a second wave of the pandemic.
Harmony also updated its FY21 production and AISC guidance following the integration of the recently-acquired Mponeng mine and related assets, plus the amended plan at Target.
Guidance was forecast to increase from 1.26-1.3 million ounces at an AISC of R690,000-710,000/kg, to 1.56-1.6Moz at an AISC of R700,000-720,000/kg.
Harmony had no progress to report, however, at its proposed Wafi-Golpu joint venture with ASX-listed Newcrest Mining in Papua New Guinea, which it recently described as a potential game-changer.
Steenkamp reiterated the partners looked forward "to re-engaging with the state of Papua New Guinea and progressing discussions on the Special Mining Lease".
Harmony shares (JSE: HAR) are trading near a mid-point in its one year range, closing up 3.4% yesterday to R57.90 to capitalise it about R36 billion (US$2.4 billion).