One off costs - including defending alleged breaches of anti-money laundering and counter-terrorism financing laws - have dragged down the profits of gambling business Tabcorp.

Tabcorp reported a first-half profit of $81.9 million, down 33 per cent on the prior corresponding period.

Underlying profit - with the effect of one-off items removed - rose 7 per cent $97.5 million.

The impairment charges of $15.6 million were largely made up of legal costs defending money laundering charges, as well as costs associated with a new betting joint venture set up with The Sun newspaper in the UK.

The civil proceedings brought against Tabcorp by the Australian Transaction Reports and Analysis Centre (AUSTRAC) under the Anti-Money Laundering and Counter-Terrorism Financing Act have so far cost the company more than $7 million.

Tabcorp said it had recently adopted an enhanced anti-money laundering program covering all its operations and has been actively working with AUSTRAC to resolve the issue as a priority.

However, it acknowledged that it is too early to determine the full financial impact of the proceedings on the company.

First half revenues rose 1.8 per cent to $1.1 billion.

The wagering and media business continued to be the core contributor, despite increased competition eroding the profitability of the traditional totalisator operation.

Overall TAB Racing revenues were up 2 per cent to $895 million.

Betting revenues on mobile devices continued to grow, accounting for 65 per cent of all digital wagering, which rose by 9 per cent to $1.9 billion.

Tabcorp continued its rollout of poker machines, with 9,550 now contracted, up from 8,820 six months earlier.

Despite the profit decline, the company boosted its interim dividend by 20 per cent to 12 cents per share.

At midday (AEDT) Tabcorp shares had tumbled 5.5 per cent to $4.27.