Congo's Progressive Property Tax Experiment Raised Revenue by 56%

Governments in poorer countries often can't tax the way rich ones do. A progressive property tax — where owners of more valuable homes pay a higher rate — sounds fair, but it is hard to administer where property records are incomplete and enforcement is thin. Many developing-country governments default to flat, proportional rates instead, on the assumption that progressivity would simply cost too much to collect.

A new study puts that assumption to the test. Working with a provincial government in a large city in the Democratic Republic of Congo, researchers randomly assigned different neighborhoods to one of two property tax schedules: a flat rate for everyone, or a progressive one where more valuable properties paid steeper rates. The progressive schedule collected 56% more revenue than the flat one.

The gains came from both ends of the property-value scale. At the top, higher official rates raised more money even though some expensive properties under-complied. At the bottom, lower rates persuaded more owners to actually pay, more than making up for the smaller amount each one owed. People, it turned out, mostly responded to their own tax bill — not to what neighbors paid, or to whether the system felt fair overall. And when the city later paired the progressive schedule with tougher enforcement on high-value properties, the system stopped being regressive in practice.

Why progressive property taxes are rare in poor countries

High-income countries lean on progressive taxation — income tax brackets, capital gains rates, estate taxes — as a matter of course. Developing-country governments mostly don't, and not because they've decided flat taxes are fairer. Progressivity requires knowing who owns what and what it's worth, then being able to enforce collection against owners who have both the means and the incentive to resist. Where property registries are outdated or missing and tax administrations are thin on staff and data, most public finance economists have assumed progressive schedules would collapse under their own administrative weight — coverage would be patchy, enforcement inconsistent, and richer owners would simply evade at higher rates than poorer ones, undoing the fairness gain and losing revenue in the process.

What the Congo experiment actually did

Six economists — Gabriel Z. Tourek, Arthur Laroche, Augustin Bergeron, Joana Naritomi, Jonathan L. Weigel, and Marina Mavungu Ngoma — partnered with a provincial government in a large Congolese city to test this directly, rather than model it theoretically. Neighborhoods across the city were randomly assigned to one of two property tax schedules: a flat, proportional rate applied uniformly regardless of property value, or a progressive schedule where the tax rate itself rose with assessed property value. Because assignment was random at the neighborhood level, differences in revenue and compliance between the two groups can be attributed to the schedule itself, not to pre-existing differences between richer and poorer parts of the city.

Where the extra revenue actually came from

The headline number is a 56% revenue increase under the progressive schedule relative to the proportional one. What makes the result more interesting than a single top-line figure is where that 56% came from: gains showed up across the entire property value distribution, not just at the top. Among the most valuable properties, the mechanical effect of a higher statutory rate raised more revenue per property even though compliance among wealthy owners dipped somewhat — some simply paid less of what they technically owed. Among lower-value properties, the opposite dynamic applied: a lower rate made the tax bill feel more worth paying, and the resulting jump in how many people actually paid more than offset the smaller amount owed per compliant owner.

What this means beyond one city in Congo

The immediate implication is narrow and empirical: progressive property taxation is not automatically self-defeating in a low-capacity administrative environment, at least not in this setting. The broader implication is about how governments think about the trade-off between fairness and feasibility. Finance ministries and municipal authorities across the developing world routinely default to flat-rate instruments — VAT, flat property levies, uniform license fees — partly out of a belief that progressive alternatives are administratively unworkable outside rich-country tax agencies. This study is direct evidence, from an actual government partnership rather than a lab or survey, that progressive design can outperform flat design on revenue grounds alone, before any fairness argument is even invoked. It also matters for how enforcement resources get allocated: the researchers found that when the city later scaled the progressive schedule citywide and paired it with enforcement specifically targeted at high-value properties, the gap between statutory and effective tax rates at the top closed — the system stopped being regressive in effective terms, not just in the rate schedule written into law.

How this fits with what we already knew

Prior research on taxation in low-income settings has mostly documented the opposite problem: attempts at progressive taxation — on income, on high-value assets — running aground on weak third-party information (no reliable employer wage reporting, no bank data-sharing, no digitized land registries) that rich-country tax agencies take for granted. Property tax is unusual in this literature because the tax base is physically observable — a building doesn't move, and its relative size and location are visible without any digital paper trail. That may be exactly why progressivity worked here when it has struggled elsewhere: assessors could rank properties by observable characteristics well enough to apply different rates credibly, even without the kind of granular financial data an income tax would require.

Experimental design

The study is a citywide field experiment conducted in partnership with a provincial government in the Democratic Republic of Congo, with a pre-analysis plan registered on the AEA RCT Registry (AEARCTR-0014314) in September 2024 and IRB approval from the University of California, Berkeley. Neighborhoods were the unit of randomization, assigned to either a proportional property tax schedule (a single rate applied to all assessed property values) or a progressive schedule (marginal rates rising with assessed value, structurally similar to an income tax bracket system but applied to property assessments instead of income). Randomizing at the neighborhood level, rather than letting owners self-select or applying the schedules city-wide sequentially, lets the researchers isolate the causal effect of the tax schedule design from confounding factors like neighborhood wealth, existing compliance culture, or enforcement capacity that happened to vary across the city for unrelated reasons.

Cross-randomized information treatments

Layered on top of the schedule randomization, the researchers also cross-randomized information treatments — different messaging sent to taxpayers about the rates. Some messages emphasized the taxpayer's own rate; others emphasized the rates other neighborhoods or property tiers faced; others framed the schedule in terms of its overall fairness. The point was to separate three possible channels through which a progressive schedule could affect compliance: taxpayers reacting to their own bill, taxpayers reacting to relative treatment versus others (a comparison or "fairness" channel), or taxpayers reacting to perceptions of the system's legitimacy as a whole. The finding was that compliance responses were driven overwhelmingly by a taxpayer's own assigned rate. Information about what others paid, or framing around the fairness of the schedule as a whole, made little independent difference. That's a methodologically useful result on its own: it suggests governments designing tax communications in similar settings can focus on making an individual's own liability and payment process clear, rather than investing heavily in fairness messaging or social-comparison framing.

Effective tax rates and the regressivity puzzle

One counterintuitive finding concerns effective tax rates — actual taxes paid as a share of property value, as opposed to the statutory rate written into the schedule. Effective rates declined as property value rose, and this pattern was most pronounced under the progressive schedule, not the flat one. In other words, in the schedule's initial rollout, the properties with the steepest statutory rates were also the ones with the biggest gap between what was legally owed and what was actually collected — a form of effective-rate regressivity sitting underneath a progressive rate structure on paper. This is an important distinction for anyone evaluating tax reforms from statutory design alone: a progressive-looking schedule can still be regressive in practice if compliance and enforcement don't scale with the size of the liability.

Enforcement changes the picture

After the initial experiment, the provincial government scaled the progressive schedule citywide and paired it with enforcement effort specifically targeted at high-value properties — the segment where the earlier effective-rate gap was largest. That combination reversed the pattern: statutory and effective rates converged, meaning the tax burden shifted more genuinely onto wealthier property owners once enforcement, not just rate design, targeted the top of the distribution. The methodological takeaway is that progressive rate design and progressive enforcement are complements, not substitutes — a progressive schedule without matching enforcement capacity at the top of the distribution risks looking progressive on paper while remaining close to flat in practice.

Study credibility and funding

The paper was pre-registered before data collection, reviewed by an institutional IRB, and disclosed funding from the Financing of Local Government Revenue Initiative (LoGRI), the Fund for Innovation in Development, USAID, the Weiss Fund, Harvard's Dean's Competitive Fund for Promising Scholarship, the Philomathia Foundation, the International Growth Center, the Swedish International Development Cooperation Agency, and the World Bank's Datax program — a mix of academic and development-finance funders with no single funder positioned to influence the result in a particular direction. The authors are affiliated with NBER's Public Economics and Development Economics programs; the paper circulated as NBER Working Paper 35536, issued July 2026.

Limitations and what's still open

The results come from one city in one country, and property tax administration varies enormously across (and within) developing countries depending on cadastral quality, local political economy, and the specific enforcement technology available. Whether a 56% revenue gain and the same top-and-bottom mechanism would replicate in a different administrative environment — a different country, a different city with a more or less developed property registry — is an open empirical question the authors don't claim to have answered. The result should be read as strong evidence that progressive property taxation is administratively viable in at least one low-capacity setting, not as a universal claim that progressivity always beats flat rates everywhere; the enforcement-pairing result in particular suggests the revenue and equity gains are conditional on state capacity being deployed deliberately at the top of the distribution, not automatic.

How to read the 56% number correctly

It's worth being precise about what the 56% figure does and doesn't say. It is a relative comparison between two randomly assigned groups of neighborhoods within the same city, over the same time period, collected by the same administration — not a before-and-after comparison, and not a claim about how much more revenue progressive taxation could raise in the abstract. That randomized, same-city, same-period design is what allows the causal claim: absent the schedule difference, the two groups of neighborhoods would be expected to generate similar revenue, so the 56% gap is attributable to the rate structure itself rather than to which neighborhoods happened to be richer or already better at complying.

Why the compliance response matters as much as the rate design

The paper's finding that low-value property owners paid more often under lower rates — enough to offset the smaller amount each owed — is a compliance-elasticity result, not just an arithmetic one. It implies that at the bottom of the property-value distribution in this setting, the binding constraint on revenue wasn't the rate itself but whether people paid at all. A schedule that lowers rates for the least valuable properties while raising them for the most valuable ones can, under the right compliance response, out-collect a uniform rate set anywhere in between — which is a substantially more actionable insight for a finance ministry than simply being told to "tax progressively."