The total surplus of U.K. defined benefit funds covered by the Pension Protection Fund's 7800 index increased 76.2% in May to £94.6 billion ($134.2 billion).
The surplus was £53.7 billion at the end of April.
A year earlier, U.K. corporate DB funds recorded a total deficit of £132.3 billion, the London-based PPF said in an update Tuesday. The PPF is the lifeboat fund for the defined benefit plans of insolvent U.K. companies.
The funding ratio increased to 105.5% as of May 31, up from 103.1% as of April 30. The funding ratio was 93.1 % as of May 31, 2020, the update said.
As of May 31, 46.1% of the 5,318 pension funds covered by the index were in deficit at a total £117.8 billion, compared with 49.3% and £135.8 billion as of April 30. As of May 31, 2020, 64.1% of pension funds were in deficit at a total £263.2 billion.
Assets were up 0.2% over the month and rose 0.1% for the year ended May 31, to £1.79 trillion.
Liabilities decreased 2.1% over the month and declined 11.7% for the year, to £1.69 trillion.
The FTSE All-Share index was up 1.1% for the month and gained 23.1% for the year ended May 31, the PPF said.
Five- to 15-year index-linked gilt yields declined 1 basis point in May but increased 27 basis points over the year.
Market conditions were relatively stable, but the change in surplus was largely attributable to a change in assumptions used by the PPF to conduct valuations of assets and liabilities of funds covered by the index, Lisa McCrory, chief finance officer and chief actuary at the fund, said in a news release accompanying the update. The change resulted in an increase in the funding ratio of 2.4 percentage points.
"So far this year we've seen an improved position for U.K. DB schemes, however we remain alert to the continuously changing environment around us, " she added.