For two Gauteng adults bringing home R30,000 and R20,000 a month, combining households at 25 rather than 35 leaves about R3.972 million more combined household wealth at 75 in the average scenario, in constant 2026 rand. The direct living-cost saving is about R1.059 million. The larger gap comes from investing that earlier saving and from avoiding expensive negative balances.
Evidence status: Modelled. Sensitivity: high. Depends on GSX:HH-001:A01, GSX:HH-001:A02, GSX:HH-001:A03, GSX:HH-001:A04. This is a modelled scenario, not a forecast, and it is household wealth rather than each person's wealth. The manuscript keeps the relationship intact and invests the surplus. The advantage can disappear or reverse if the shared household costs almost as much as two homes, if the saving is consumed, or if separation costs exceed the accumulated benefit. Cohabitation here is a shared household, not a marriage result.
C01
Related questions
What is the lifetime household comparison between living together and maintaining separate households?
How does the timing of cohabitation change the cost of living and saving?
5
Assumptions
Assumptions
These are the registered model assumptions. A result stays conditional on the ones a claim names.
A01Two Gauteng earnersThe household is two adults in Gauteng with take-home pay of R30,000 and R20,000 a month. The results are combined household wealth, not each person's legal ownership.30000 constant 2026 rand per month, higher take-home pay
A02Ten-year difference in household timingThe Early couple combines adequate households at 25. The Later couple combines them at 35. From 35 onward the model gives both the same housing arrangement, income, expenses, shocks, and retirement assumptions.10 years
A03Average-case returns and costsIn the average case, real salary growth and real living-cost growth are both 0.75% a year. The net real investment return is 3% a year after fees and tax drag. The initial monthly cohabitation dividend is R8,500.3 percent net real return per year
A04Surplus is investedThe model invests the available surplus. It does not spend that surplus on a higher lifestyle.qualitative not a scalar
A05The relationship remains intactBoth relationships remain intact through the simulation. Separation, custody, maintenance, and a second replacement home are not given a numeric cost.qualitative not a scalar
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Model
Model
The registered model statement. It is a scenario model, and the manuscript remains the full specification.
M01Lifetime household-timing modelThe model follows two household paths from age 25 to 75 in constant 2026 rand. They differ in when they combine households. After 35 their housing arrangement matches, so the remaining gap comes from returns on the earlier balance or from the cost of a negative balance. Best, average, and worst cases change growth, returns, shocks, children, and housing.GSX:HH-001:M01
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Results
Results
Modelled scenario results. They are not forecasts.
R013972000 constant 2026 randIn the average case, the Early household holds R3.972 million more combined wealth at 75 than the Later household, in constant 2026 rand.Average case, age 75, early consolidation minus later consolidation
R021059000 constant 2026 rand of living costs avoidedIn the average case, the Early household spends about R1.059 million less on living costs over the model. At 35, before the later years are financially identical, its lead is R1.188 million.Average case, lifetime living costs and age-35 lead
R0311287000 constant 2026 rand, best-case lead at 75At 75 the Early household's lead is R11.287 million in the best case and R1.882 million in the worst case. In the worst case both positions are large funding gaps: about -R16.346 million and -R18.228 million.Best case and worst case at age 75
Sensitivity
High · 2
Moderate · 0
Low · 0
Limitations
This is a modelled scenario, not a forecast, and it is household wealth rather than each person's wealth. The manuscript keeps the relationship intact and invests the surplus. The advantage can disappear or reverse if the shared household costs almost as much as two homes, if the saving is consumed, or if separation costs exceed the accumulated benefit. Cohabitation here is a shared household, not a marriage result.
Negative amounts are unmet consumption if the household does not change course. They are not a statement that a bank would finance the shortfall. The worst case cannot repair stagnant earnings, repeated unemployment, weak returns, or inadequate retirement income.
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Claims
Claims
Each claim names the assumptions it uses and the limitation that travels with it.
C01GSX:HH-001:C01For two Gauteng adults bringing home R30,000 and R20,000 a month, combining households at 25 rather than 35 leaves about R3.972 million more combined household wealth at 75 in the average scenario, in constant 2026 rand. The direct living-cost saving is about R1.059 million. The larger gap comes from investing that earlier saving and from avoiding expensive negative balances.Modelled · high sensitivity
C02GSX:HH-001:C02Across the manuscript's three scenarios, earlier household combination still leaves the stronger position at 75. The lead is R11.287 million in the best case, R3.972 million in the average case, and R1.882 million in the worst case. In the worst case that lead only narrows two large funding gaps.Modelled · high sensitivity
Sources and reproducibility
The PDF and complete Markdown source are both published.
Full manuscript: 5 806 words across 39 indexed headings. Source checksum: 9ac1edb15cae…. Code recorded: yes. Data recorded: yes. Environment recorded: no. Published files: 2. the published statement does not rely on a recorded random seed A public code repository is not published.
