The firm said the improvement was broad-based by geography, consumer health and hygiene led, and aided by a favourable flu season.
Reckitt is trying to boost its presence in the consumer health sector, which has been growing fast amid increased demand for over-the-counter remedies and health products due to a greater awareness of health, aging populations in developed markets and rising incomes and urbanisation in emerging markets.
Like-for-like sales had also risen 5 percent in the first quarter, while analysts on average had been expecting first half growth of 4.6 percent, according to a company compiled consensus.
Reckitt Benckiser's adjusted operating margin rose 160 basis points to 21.9 percent in the first half, while adjusted diluted earnings per share increased 7 percent to 99 pence.
"I am pleased with our first half results, they once again confirm that our strategic focus on consumer health and hygiene is delivering sustainable growth and outperformance," said Chief Executive Rakesh Kapoor.
The group is now targeting full-year like-for-like net revenue growth of 4-5 percent and second half moderate to "nice" adjusted operating margin expansion.
It was previously forecasting 4 percent like-for-like sales growth.
Shares in Reckitt, up 18 percent over the last year, closed Friday at 5,908 pence, valuing the business at 42 billion pounds.
The firm is paying an interim dividend of 50.3 pence, in line with guidance.