Deficits and surpluses, cyclical against structural deficits, automatic stabilisers as a movement along the budget-balance line and discretionary policy as a shift, how deficits add to the debt, the debt-ratio arithmetic, debt interest, fiscal rules and whether the debt matters. Through the UK public finances of 2025–26.
In the financial year to March 2026 the UK public sector spent £1,363bn, £72bn more than the year before, on public services, benefits and debt interest. Revenue did not keep up, and the government borrowed £132bn to fill the gap: 4.3% of GDP, down from 5.2% the year before and £0.7bn below the Office for Budget Responsibility’s forecast. The deficit on day-to-day spending alone was £51bn.
Public sector net debt reached £2.91 trillion, 93.8% of GDP, a level last seen in the early 1960s, and up 0.6 points on the year despite the lower borrowing. Debt interest cost £106bn in 2024–25, against £39bn in 2019–20. The OBR expects borrowing to fall to 1.6% of GDP by 2030–31, if the Chancellor’s plans hold, and warned that the next Budget would be as hard as the last.
How does a deficit become a debt, how much of it is the economy’s fault rather than the government’s, and does it matter?
Source: ONS, Public sector finances, March 2026 (23 April 2026); OBR, Economic and fiscal outlook, March 2026 (3 March 2026).
The budget balance is government revenue minus spending in a year. Spending above revenue is a budget deficit (public sector net borrowing); revenue above spending is a surplus. The current budget excludes investment: a current deficit means borrowing to pay for day-to-day running costs.
The national debt (public sector net debt) is the stock of past borrowing not yet repaid. Each year’s deficit adds to it. It is measured against GDP because what matters is the ability to service it.
The deficit has two parts. The cyclical deficit comes from the state of the economy: in a recession tax receipts fall and benefit spending rises without any change in policy, through the automatic stabilisers. The structural deficit is what would remain with the economy at potential output: the part that only a change in tax or spending, discretionary fiscal policy, can remove.
The debt ratio rises when the deficit (as a share of GDP) exceeds the debt ratio times the growth rate of nominal GDP, and falls when it is smaller. Growth and inflation shrink the ratio; deficits and high interest rates raise it.
In the year to March 2026 the UK government spent £1,363bn and borrowed £132bn to cover the gap. The national debt reached £2.91 trillion, 93.8% of GDP.
Borrowing fell by £20bn on the year before and was the lowest for three years.
So why did the debt, measured against the size of the economy, still go up?
A smaller deficit is still a deficit: £132bn of new borrowing was added to the pile. The debt-to-GDP ratio falls only when nominal GDP grows faster than the debt, and with borrowing at 4.3% of GDP and the economy growing more slowly than that, the ratio edged up from 93.2% to 93.8%.
The diagram puts the **budget balance** as a share of GDP against real GDP. The line **B1** slopes up: the higher output is, the more tax comes in and the less goes out in benefits, with no decision taken. Those are the automatic stabilisers. The vertical line marks **Yfe**, potential output, where the economy is neither in recession nor overheating.
Check: The budget balance line slopes upwards. This is because, as real GDP rises:
Income tax, VAT and corporation tax all rise with incomes and spending; unemployment benefit falls as jobs return. No decision is needed: the automatic stabilisers.
Read the balance at Yfe: a deficit of 2% of GDP even with the economy at full stretch. That is the structural deficit. It will not disappear as the economy recovers, because the economy has already recovered. Closing it takes a decision: higher taxes or lower spending. The OBR’s job is to estimate how much of the UK’s 4.3% is structural, which depends on an unobservable Yfe.
Check: At potential output Yfe the balance on B1 is a deficit of 2% of GDP. This is the:
With output at potential there is no recession to blame. A deficit at Yfe reflects the balance of tax and spending decisions.
A recession takes output to **Y recession**. Moving down B1, the deficit widens to 4.4%: receipts fall, benefits rise. The extra 2.4 points are cyclical. They are the stabilisers at work, cushioning the downturn by letting the government borrow instead of households cutting back. As output recovers they close on their own. Cutting spending to remove them would deepen the recession.
Check: In a recession output falls to Y recession and the deficit on B1 is 4.4% of GDP. The cyclical deficit is:
Total deficit = structural + cyclical. 4.4 − 2.0 = 2.4 points of GDP are due to the downturn and will close as output recovers.
Now discretionary fiscal policy. The Chancellor raises taxes and trims spending by 2% of GDP. The line shifts up to **B2**: at Yfe the budget balances; in a recession the deficit is 2.4% instead of 4.4%. The November 2025 Budget was a shift of this kind, raising taxes to meet the fiscal rules. The cost: the tightening itself lowers aggregate demand, which is why the timing matters.
Teacher tip: Exam answers confuse the two every year. Movement along the line = automatic stabilisers, caused by the cycle. Shift of the line = discretionary policy, caused by a Budget. Say which one you mean.
Check: The government raises taxes and cuts spending by 2% of GDP. On the diagram this:
Discretionary fiscal policy changes the balance at every level of output, so the line shifts. The slope, set by the tax and benefit system, is unchanged.
From deficit to debt. Every deficit adds to the **national debt**; what matters is debt relative to GDP. The ratio rises when the deficit outruns growth: change in ratio ≈ deficit − (debt ratio × nominal growth). Debt at 94%, nominal growth 4%: growth shaves 3.8 points a year; a 4.3% deficit more than offsets it. Hence 93.8% and rising.
Check: The debt ratio is 94% of GDP, the deficit is 4.3% of GDP and nominal GDP grows 4% in the year. Roughly, the debt ratio:
Growth shrinks the ratio by debt × growth (about 3.8 points); the deficit adds 4.3. Net, up about 0.5. The UK ratio rose from 93.2% to 93.8%.
Does the debt matter? For: debt interest over £100bn a year is money not spent on schools; markets can demand higher yields, as in September 2022; a country at 94% has less room to borrow in the next crisis. Against: the government borrows in its own currency, rolls debt over, and in a boom the line crosses into surplus by itself.
Check: Which is the strongest argument that a high national debt matters?
Governments roll debt over rather than repay it, but interest is a real annual cost, and a high ratio limits what can be borrowed when a pandemic or war arrives.
The 4.4% deficit at Y recession is labelled structural. It is the total: 2% structural plus 2.4% cyclical. The structural deficit is read at Yfe, not at the bottom of the cycle. Treating the whole 4.4% as structural would lead to a tightening twice as large as needed.
In 2025–26 the UK borrowed £132bn, 4.3% of GDP, and public sector net debt reached 93.8% of GDP. Explain the difference between cyclical and structural deficits, and evaluate whether the government should prioritise reducing the national debt.
A budget deficit is the gap between government spending and revenue in a year; the national debt is the stock of past deficits still outstanding. In 2025–26 the UK borrowed £132bn, 4.3% of GDP, and the debt stood at 93.8% of GDP. The ratio to GDP matters because it measures the burden relative to the capacity to service it.
The deficit has two parts. The cyclical deficit arises from the economic cycle: in a downturn tax receipts fall and benefit spending rises automatically, a movement along the budget-balance line, and the reverse happens in a boom. These automatic stabilisers cushion demand without any decision. The structural deficit is what would remain with the economy at potential output; it reflects the underlying balance of tax and spending and can only be removed by discretionary policy, which shifts the whole line. Distinguishing the two requires an estimate of potential output, which is uncertain, but it decides how much of a deficit policy must address.
The debt ratio rises when the deficit, as a share of GDP, exceeds the debt ratio multiplied by nominal growth. With debt near 94% and nominal growth of about 4%, a deficit above about 3.8% of GDP raises the ratio, which is why it edged up despite lower borrowing. Debt interest of £106bn in 2024–25, against £39bn in 2019–20, shows the cost of a high ratio when interest rates rise.
There is a case for prioritising the debt: interest crowds out spending on services, markets can punish a loss of confidence, as in September 2022, and a country already at 94% has less room to borrow in the next crisis. **However,** tightening to remove a cyclical deficit deepens the downturn that caused it, and the structural part is smaller than the headline. Borrowing to invest in capacity that raises potential output can pay for itself in future receipts, which is why the fiscal rules target the current budget rather than all borrowing. And the arithmetic shows that growth, not austerity, is the main route to a lower ratio: a rule met by cutting investment damages the growth that would make the debt sustainable. The government should reduce the structural current deficit steadily, protect investment, and accept that the cyclical part will close by itself.
Public finances: Office for National Statistics, public sector finances, March 2026 (released 23 April 2026); Office for Budget Responsibility, Economic and fiscal outlook, March 2026. The budget-balance line on the diagram is for an invented economy, chosen so the numbers are clear. Diagrams drawn with Rough.js and perfect-freehand, both MIT licensed.