A Newsquawk Budget preview published on 26 October expects the OBR to leave the Chancellor, John Healey, with about £15bn of headroom, down from £23.6bn in March. It puts the starting point before any policy decisions at £10bn to £12bn.
The preview breaks the estimate down. It says gilt yields are more than 50 basis points higher than in March, a hit of about £6bn. Market pricing for Bank Rate, against a March assumption of an average of 3.6% to 2030, takes off about £4bn. A weaker growth path costs about £2bn.
The main offset, Newsquawk says, would be an upgrade of 30 to 60 basis points to the wage forecast for 2027. That would add about £5bn to £10bn net through tax receipts.
It says every 50,000 downgrade to net migration cuts headroom by about £4bn. The OBR assumed 235,000 a year in March, while the ONS's current view is 171,000.
On debt interest, it says each percentage point on yields adds £8.4bn by 2029-30. It cites ING predicting debt interest could be more than £11bn higher by then.
The £23.6bn March figure matches the headroom at the March fiscal update. The rest is analyst expectation, not a leak or an OBR figure, and has not been independently checked.