Ichthys' production has been delayed from towards the end of December 2016, when it was initially expected to go online, to the July-September quarter in 2017.
A recent technical evaluation of the entire LNG production system also prompted Inpex to lift Ichthys' annual LNG production capacity by about 6% from 8.4 million tonnes per annum to 8.9MMtpa.
Inpex said Ichthys was about 74% complete as of June this year, but the revised productions start-up and "other factors" will increase the LNG project's investment by a maximum of 10%, which would bring the $US34 billion price tag to approximately $US37.4 billion.
The Japanese major said the updated schedule also reflected the expectation of a shortened time frame between the start of production and the point where stable production is reached.
"The Ichthys LNG project is a world-class project with an expected operational life of at least 40 years," Inpex CEO Toshiaki Kitamura said.
"All the LNG initially planned to be produced from the project has been sold.
"Of this, about 70% of the LNG is set to be supplied to Japan, and this is expected to further contribute to the long-term, stable supply of energy to the country and improve Japan's energy procurement risk management.
"The project is also expected to make a significant contribution to the social and economic development of Australia, one of the world's foremost producers of energy.
"Inpex will guide the Ichthys LNG project to success, working closely with its project partners, local communities, Australia's federal government as well as the governments of Western Australia and the Northern Territory, other project stakeholders and the wider Australian public to seek their continued understanding and support."
The company added that the impact of the production start schedule update, "if any", on the consolidated financial results for the year ending March 31, 2016 was "expected to be minimal".
Inpex said it planned to cover the costs of the project through its own funds as well as external loans as originally scheduled.
Inpex, which operates Ichthys, has a 62.245% stake in the project alongside French super-major Total (30%), CPC Corporation Taiwan (2.625%), Tokyo Gas (1.575%), Chubu Electric Power (0.735%) and Toho Gas (0.42%).
The project involves liquefying natural gas lifted from the Ichthys gas-condensate field offshore Western Australia at an onshore gas liquefaction plant constructed in Darwin and producing and shipping 8.9MMtpa of LNG and 1.6MMtpa of LPG, along with about 100,000 barrels of condensate per day at peak.
Inpex acquired the exploration permit in the block where the project is located in 1998 and announced final investment decision in January 2012.
