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Is a flat-rate income tax a good idea?

At an event at the London Palladium on 6 December staged to protest against elements in the recent Budget, the Conservative leader, Kemi Badenoch, was asked whether she would introduce a flat-rate income tax if the Conservatives were returned to government. She replied that it was a very attractive idea. But first the economy would need ‘rewiring’ so that the tax burden could be lightened.

A flat-rate income tax system could take various forms, but the main feature is that there is a single rate of income tax. The specific rate would depend on how much the government wanted to raise. Also it could apply to just income tax, or to both income tax and social insurance (national insurance contributions (NICs) in the UK), or to income tax, social insurance and the withdrawal rate of social benefits. It could also apply to local/state taxes as well as national/federal taxes.

Take the simplest case of a flat-rate income tax with no personal allowance. In this system the marginal and average rate of tax is the same for everyone. This is known as a proportional tax.

Most countries have a progressive income tax system. This normally involves personal allowances (i.e. a zero rate up to a certain level of income) and then various tax bands, with the marginal rate rising when particular tax thresholds are reached. In England, Wales and Northern Ireland, there are three tax bands: 20%, 40% and 45%. Thus the higher a person’s income is, the higher their average rate of tax.

A regressive tax, by contrast, would be one where the average rate of tax fell as incomes rose. The extreme case of a regressive tax would be a lump-sum tax (such as a TV or other licence), which would be same absolute amount for everyone liable to it, irrespective of their income. This was the case with the ‘poll tax’ (or Community Charge, to give it its official title), introduced by Margaret Thatcher’s government in 1989 in Scotland and 1990 in the rest of the UK. It was a local tax, with each taxpayer taxed the same fixed sum, with the precise amount being set by each local authority. After protests and riots, it was replaced in 1993 by the current system of local taxation (Council Tax) based on property values in bands.


Figures 1 and 2 illustrate these different categories of tax: see Figure 11.12 in Economics, 12th edition. (Click here for a PowerPoint.) Income taxes in most countries are progressive, although just how progressive depends on the differences between the tax bands and the size of personal tax-free allowances. A flat-rate income tax with no allowances is shown by the black line in each diagram, the slope in Figure 1 and the height in Figure 2 depending on the tax rate.

Arguments for a flat-rate income tax

Generally, arguments in favour of flat-rate taxes come from the political right. The two main arguments in favour are tax simplification and incentives.

Advocates argue that a flat tax system makes tax collection easier and makes tax evasion harder. If there are no exemptions, then it can be easier to check that people are paying their taxes and working out the correct amount they owe. It is argued that, in contrast, high tax rates on top earners can encourage tax evasion.

Flat taxes can also be part of a drive to reduce the size of the informal economy. As the VoxEU article states:

Unlike progressive taxes, which include complex and numerous exceptions left to the tax collectors’ discretion, the flat tax is clear cut. In combination with the low rate, its simplicity considerably reduces the stimuli for being informal.

Several post-communist countries in Eastern Europe adopted flat taxes, but for most they were seen as a temporary measure to reduce the informal sector and clamp down on tax evasion. Most have now adopted progressive taxes, with the exceptions of Bulgaria and until recently Russia.

The second major argument is that lower taxes for higher earners, especially for entrepreneurs, can act as a positive incentive. People work harder and there is more investment. The argument here is that the positive substitution effect from the lower tax (work is more profitable now and hence people substitute work for leisure) is greater than the negative income effect (lower taxes increase take-home pay so that people do not need to work so much now to maintain their standard of living).

Then there is the question of tax evasion. With high rates of income tax for top earners, such people may employ accountants to exploit tax loopholes and hide earnings. This could be seen as highly unfair by middle-income earners who are still paying relatively high rates of tax. Even though a move to flat taxes is likely to mean a cut in tax rates for high earners, the tax take from them could be higher. There is evidence that post-communist and developing countries that have adopted flat taxes have found an increase in tax revenues as evasion is harder.

The Laffer curve is often used to illustrate such arguments that high top tax rates can lead to lower tax revenue. Professor Art Laffer was one of President Reagan’s advisers during his first administration (1981–4): see Box 11.3 in Economics, 11th edition. Laffer was a strong advocate of income tax cuts, arguing that substantial increases in output would result and that tax revenues could consequently increase.

The Laffer curve in Figure 3 shows tax revenues increasing as the tax rate increases – but only up to a certain tax rate (t1). Thereafter, tax rates become so high that the resulting fall in output more than offsets the rise in tax rate. When the tax rate reaches 100 per cent, the revenue will once more fall to zero, since no one will bother to work. (Click here for a PowerPoint)

However, as Box 11.3 explains, evidence suggests that tax rates in most countries were well below t1 in the 1980s and certainly are now, given the cuts in income tax rates that have been made around the world over the past 20 years.

Arguments against flat-rate income taxes

The main argument against moving from a progressive to a flat-rate income tax in an advanced country, such as the UK, is that is would involve a large-scale redistribution of income from the poor to the rich. If the tax were designed to raise the same amount of revenue as at present, those on low incomes would pay more tax than now, as their tax rate would rise to the new flat rate. Those on high incomes would pay less tax, as their marginal rate would fall to the new flat rate.

If a new flat-rate tax in the UK also replaced national insurance contributions (NICs), then the effect would be less extreme as NICs are currently initially progressive, as there is a personal allowance before the 8% rate is applied (on incomes above £12 570 in 2024/25). But above a higher NI threshold (£50 270 in 2024/25), the marginal rate drops to 2%, making it a regressive tax beyond that level. Figure 4 shows tax and NI rates in England, Wales and Northern Ireland for 2024/25. (Click here for a PowerPoint.)

Nevertheless, even if a new flat-rate tax replaced NICs as well as varying rates of income tax, it would still involve a large-scale redistribution from low-income earners to high-income earners. The effect would be mitigated somewhat if personal allowances were raised so that the tax only applied to mid-to-higher incomes. Then the redistribution would be from middle-income earners to high-income earners and also somewhat to low-income earners: i.e. those below, or only a little above, the new higher personal allowance. If, on the other hand, personal allowances were scrapped so that the flat tax applied to all incomes, then there would be a massive redistribution from people on low incomes, including very low incomes, to those on high incomes.

One of the arguments used to justify a flat-rate tax is that its simplicity would ensure greater compliance. But in an advanced country, compliance is high, except, perhaps, for those on very high incomes. Most people in the UK and many other countries, have tax deducted automatically from their wages. People cannot avoid such taxes.

As far as the self-employed are concerned, they file tax returns online and the software automatically works out the tax due. There are no complex calculations that have to be performed by the individual. There is come scope for tax evasion by charging various expenditures to the business that are really personal spending, but the tax authorities can ask for evidence and sometimes do, with penalties for false claims.

What tax evasion does take place, could still do so with a flat tax. At a rate of, say, 20%, it would still be financially beneficial for a dishonest person to lie if they could get way with it.

Conclusions

If the government did try to introduce a flat-rate income tax, there would probably be an outcry. Also, as some rich people would gain a very large amount of money, the number of people gaining would be lower than the number losing if the total revenue raised were to remain the same. In other words, it would be politically difficult to achieve if the number of losers exceeded the number of gainers.

It is true that if the top rate of income tax were very high, then reducing it might bring in more revenue. But at 45%, or 47% if you include NICs, the top marginal rate in the UK is relatively low compared with other countries. In 2024, the UK had the second lowest top rate of tax out of Western European countries (behind Norway and Switzerland) and only the 16th highest out of 33 European countries when Central and Eastern European countries are also included (see the final ink below under ‘Information’). Reducing the UK’s top rate would be unlikely to bring in more revenue and would redistribute income to high-income earners.

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Questions

  1. What are the income and substitution effects of changing tax rates?
  2. Explain the Laffer curve and consider whether it is likely to be symmetrical.
  3. Discuss the desirability of having a flat tax set at a relatively high rate (say 25%) with tax-free personal allowances up to the level of income considered to be the poverty threshold. (In the UK the poverty threshold is often defined as 60% of median income.)
  4. In the London Palladium event where Kemi Badenoch stated that flat taxes were a very attractive idea, she also said that ‘We cannot afford flat taxes where we are now. We need to make sure we rewire our economy so that we can lighten the burden of tax and the regulation on individuals and on those businesses that are just starting out, in particular’. What do you think she meant by this?
  5. Find out what Bulgaria’s experience of a flat tax of 10% has been.