The collective deficit of defined benefit (DB) schemes remained at £460bn from the end of August to the end of September, according to PwC's Skyval index.
The measure, which tracks roughly 5,800 schemes, revealed assets decreased from £1.6trn to £1.5trn by the end of September, while liabilities remained the same at £2trn.
Funding levels fell slightly, from 77.3% to 76.8% over the course of the month.
The consultancy's index is calculated on a basis of the funding measures used to work out cash contributions needed from sponsoring employers, and uses publically available data such as that held by the Pension Protection Fund.
At the end of August, the deficit had small increased by 10% from the end of the previous month.
The firm's chief actuary Steven Dicker said the increase of long-term interest rates as measured by government bond yields over September has led to the £50bn reduction in liabilities.
He added: "There was no impact on the deficit due to falling asset values over the month.
"The swing in the size of deficit from month to month is sensitive to small market movements, as demonstrated by the month-to-month volatility."
IAS 19 accounting deficit
A separate index published by JLT Employee Benefits showed the funding position of DB schemes under the IAS 19 standard accounting measure, used in company reports and accounts.
It revealed all private sector schemes saw a deficit decrease of £25m, down from £199bn from the end of August to the end of September.
Assets stayed the same, at £1.6trn over the month, and liabilities decreased from £1.8trn to £1.7trn.
Meanwhile, the total funding level for DB schemes rose by 1 percentage points, from 89% by the end of September.
The situation has vastly improved compared to 12 months ago, when there was a £314bn deficit, and 83% funding level.
A similar story played out for FTSE 350 companies, which saw funding levels increase from 86% by the end of September 2016, to 93% by September 2017, while deficits fell from £123bn to £57bn.
The firm's director Charles Cowling said: "Despite a political backdrop which continues to be problematic, with concerns over North Korea and Brexit, among many; despite concerns over rising inflation; despite many market worries and woes; and despite Mark Carney saying this week that the Bank of England cannot be expected to solve every economic problem in the UK, the funding position of DB pension schemes is showing signs of positive improvement, after a traumatic few years.
He added the total deficit for schemes of FTSE 100 companies being back below the £50bn level (to £45bn) is good news.
"This good news comes on the back of equity markets holding up well, inflation numbers that are as bad as some expected, longevity improvements slowing down and best of all (for pension schemes at least) a sign that at last interest rates may be on the rise again, after nearly 10 years of painful reductions."
But, he also pointed out that challenges still remain.
"Pension schemes which are carrying out actuarial valuations in 2017 are likely to show bigger deficits than in 2014 and trustees will therefore be knocking on the finance director's door asking ‘more please'."
However, he said a positive move is the International Accounting Standards Board's (IASB) recent decision to ‘perform further work to assess whether it can establish a more principles-based approach in IFRIC 14 for an entity to assess the availability of a refund of a surplus'.
He said this means the feared changes which could have seen tens of billions of pounds added to the pension liabilities, showing in the balance sheets of UK companies, has been postponed - at least for now.
"Trustees and finance directors may wish to take advantage of these slightly calmer waters to explore opportunities to offload and settle pension liabilities," he added.
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