With roughly six months to go to the adoption of one of one of the biggest accounting changes in a generation, more than one-fourth of Fortune 500 filers still had not figured out how they will be affected by the new rules as of April and May.

Only 1 percent of the Fortune 500 say their adoption of new revenue recognition accounting rules will have a material effect on the company’s financial statements, according to a PwC analysis, while 54 percent say definitively that the effect will be immaterial. Another 17 percent have provided some qualitative disclosures about the expected effect of adoption, but no materiality call and no hard data.

Companies have been facing massive new rules overhauling how they are to recognize revenue in financial statements for several years. The Financial Accounting Standards Board developed the standard over more than a decade and delivered the final text in mid-2014. After FASB issued some clarifications and deferred the effective date by one year, public companies are required to adopt the new standards and begin reflecting the new revenue recognition method on Jan. 1, 2018.

The Securities and Exchange Commission has given companies plenty of reminders that they are required under Staff Accounting Bulletin No. 74 to give investors early warning about the expected effect of adopting new accounting rules in a future period. PwC recently shared its analysis of quarterly and annual disclosures filed by Fortune 500 companies from April 1 to May 26, showing 28 percent of those companies were still saying nothing except that they were continuing to evaluate the expected effect.

In the PwC analysis, only 10 percent of companies said they would adopt the new rules following the full retrospective method, so they will present three years worth of data under the new accounting; 45 percent said they would adopt under the modified retrospective method permitted in the standard, which allows presentation of historical information using cumulative adjustments. Another 45 percent said they had not yet determined their method of adoption.

In addition to studying SAB 74 disclosures about revenue recognition, PwC also took note of Fortune 500 disclosures regarding other big accounting changes on the horizon. New rules on how to account for leasing activity take effect in 2019, followed by new rules on how to reflect credit losses in 2020.

With respect to leasing, PwC found 60 percent of the Fortune 500 offered no concrete information about how the new rules would affect the company’s financial, except to warn investors that the rules were coming and the company was evaluating and projecting the impact. Of the remaining companies, 19 percent said they expected a material impact and 4 percent said they expected an immaterial effect; 17 percent provided only qualitative disclosures but nothing quantitative.

As for credit impairments, where companies will be required in 2020 to adopt a more forward-looking approach to arrive at “current expected credit loss” data, 87 percent said they were still evaluating how they will be affected. Only 2 percent said the impact will be material, while 6 percent said the impact will be immaterial; 5 percent gave some qualitative description but nothing more.