Pension deficits of FTSE 350 organisations have increased at an average rate of more than £2 billion a day during August, according to research by Towers Watson.
The firm calculated that the aggregate deficit in FTSE 350 firms' defined benefit (DB) pension schemes has increased by £21 billion so far this month, from £52 billion at the end of July to £73 billion when markets closed on 10 August.
Assets have fallen from £506 billion to £480 billion, while liabilities have fallen from £558 billion to £553 billion.
John Ball, head of UK pensions at Towers Watson, said: "Until Wednesday, more than half of the drop in asset prices this month had been offset by a fall in liabilities, mainly because a dampening of inflation expectations meant organisations could budget for smaller pension increases.
"However, this has now been largely cancelled out by a sharp fall in corporate bond yields, which makes pension obligations on organisation balance sheets look bigger under accounting rules.
"As a result, liability changes are no longer shielding organisations from the impact of asset price falls.