“Fiscal headroom” is the margin between the Government's fiscal rule and the Office for Budget Responsibility's central forecast. It is not cash sitting in an account and it is not a fixed spending allowance. It is a forecast margin that can move materially when the OBR changes its assumptions for growth, tax receipts, welfare, interest rates or debt interest.
The latest formal OBR assessment of the fiscal rules was at the November 2025 Budget. It estimated that the current-budget rule would be met by a margin of £22 billion in 2029-30. The supplementary rule for public sector net financial liabilities was met by a margin of about £24 billion.
There is an important 2026 wrinkle: the OBR's March 2026 Economic and fiscal outlook updated the economic and public-finance forecast but did not reassess performance against the fiscal rules. Following changes to the Charter for Budget Responsibility, the formal rules assessment is now made once a year at the Budget. The next official assessment is therefore due with the 28 October 2026 Budget.
What does “£22 billion of headroom” actually mean?
The Government's fiscal mandate is for the current budget to be in balance or surplus in the target year. In the November 2025 central forecast, the OBR projected a current-budget surplus of roughly £22 billion in 2029-30. That difference between the rule boundary and the central forecast is what is normally described as headroom.
It should not be read as £22 billion the Chancellor can automatically spend. Forecasts move. The OBR noted that the £22 billion margin was close to its average pre-measures revision to borrowing four years ahead. In other words, a forecasting change of a historically ordinary size could absorb most or all of the margin without any new policy decision.
Why the March 2026 forecast did not produce a new headroom number
The March 2026 EFO still updated borrowing, debt, growth, inflation and the wider fiscal outlook. But the OBR explicitly said that it was not required to assess the fiscal mandate at that Spring forecast because the Government had moved to one formal fiscal-rule assessment a year, at Budgets.
That means there is no authoritative “March 2026 headroom” figure to substitute for the November number. Analysts can model what subsequent economic and market moves may have done to the margin, but that is an estimate rather than the OBR's formal rules assessment.
What can move fiscal headroom?
Growth and productivity matter because stronger nominal incomes and company profits can raise tax receipts, while weak productivity lowers the economy's sustainable tax base. The OBR's November 2025 sensitivity work showed how large that risk can be: weaker productivity could move the current budget from surplus into deficit, while stronger productivity could create substantially more margin.
Interest rates and gilt yields matter because the UK has a large stock of debt and a meaningful share of debt interest responds relatively quickly to market rates and inflation. In its November 2025 analysis, the OBR estimated that a one percentage point increase in Bank Rate and gilt yields could reduce the current-budget surplus by about £16 billion in the target year. That is why the gilt market matters directly to fiscal policy, not just to investors. See Briefed's gilt-yield explainer.
Inflation cuts both ways. Higher nominal prices and wages can lift tax receipts, but inflation-linked debt interest and indexed spending can rise too. The composition and persistence of inflation therefore matter more than the headline number alone.
Policy choices obviously matter as well. Tax rises, spending reductions or stronger receipts can increase headroom; tax cuts and additional current spending usually reduce it unless offset elsewhere. The OBR also models indirect effects, because policy can change growth, wages, consumption and therefore the tax base.
What does the March 2026 forecast say about the backdrop?
The March 2026 OBR forecast described the fiscal context as challenging. It expected real GDP growth of 1.1% in 2026 before growth averaged around 1.6% over the rest of the forecast. Public sector net borrowing was projected to fall over time, while public sector net debt was expected to remain around the mid-90s as a share of GDP.
The Spring forecast was broadly similar to November in its central fiscal path, but the absence of a formal rules test is precisely why it is better to keep the concepts separate: the fiscal forecast was updated; official fiscal-rule headroom was not.
Why fiscal headroom matters for UK markets
Headroom matters because a small margin can make fiscal policy more sensitive to changes in gilt yields, growth forecasts or tax receipts. If the OBR's forecast deteriorates before a Budget, the Chancellor may need tax or spending measures simply to remain inside the rule. A larger margin gives more room to absorb adverse forecast changes without an immediate policy response.
For gilts, the relationship runs both ways. Higher yields can worsen the fiscal arithmetic through debt-interest costs, while a fiscal package that markets judge to increase borrowing risk can itself put upward pressure on yields. Sterling can also respond to the interaction between fiscal credibility, growth expectations and relative interest rates.
What to watch before the October Budget
The next formal answer arrives on 28 October 2026, when the OBR is scheduled to publish its Autumn Economic and fiscal outlook alongside the Budget. Before then, the useful moving pieces are gilt yields, Bank Rate expectations, inflation, labour-market data, nominal GDP and tax-receipt performance.
For the debt stock behind the rules, see who owns UK government debt and how it is measured. For the market-price channel, see UK gilt yields. For the growth assumptions that feed receipts, see the UK growth tracker and GDP per person.
Primary sources
- Office for Budget Responsibility: Economic and fiscal outlook, November 2025.
- Office for Budget Responsibility: Economic and fiscal outlook, March 2026.
- HM Treasury: Budget 2026 will be held on 28 October 2026.
Checked 11 September 2026. Latest formal fiscal-rule assessment: 26 November 2025. Latest OBR economic and fiscal forecast: 3 March 2026. Next OBR forecast and formal Budget assessment: 28 October 2026.