The PropKaki Affordability Clock™
The PropKaki Affordability Clock is the years-of-income yardstick for Singapore public housing: the price of the median HDB resale flat divided by the median household's gross annual employment income, recomputed with every official income and price release. This page is the metric's permanent definition — its formula, deliberate omissions and version history. Current readings live on the Housing Affordability Tracker.
Definition
For each calendar year covered by both input series, the Clock reads the number of years of the median resident household's gross employment income equal to the price of the median HDB resale flat. Two readings are published: the median 4-room flat (Singapore's most-traded type, the headline) and the median resale flat across all flat types. The Clock is a comparability tool across years — it is deliberately not a mortgage calculation, and it carries no affordability verdict.
Computation
price(y) = median HDB resale price, year-end (completed year's Q4 median)
Clock(y) = price(y) ÷ income(y), rounded to one decimal place
Income is nominal, gross, and includes employer CPF contributions, exactly as published by the Singapore Department of Statistics. HDB medians are computed by PropKaki from every resale registered with HDB and annualised to each completed year's fourth-quarter value, per the tracker family's frequency rule. The two series are joined on matching years only — no interpolation, no estimates, no forecasts.
What the Clock deliberately omits
The Clock uses gross income before CPF Housing Grants (up to six figures for eligible resale buyers), CPF usage and mortgage interest — and it prices resale flats, not the subsidised BTO flats where most first-time buyers start. Each omission is deliberate: every one of those adjustments depends on assumptions that change year to year, and embedding them would make the series incomparable across time. The omissions are stated wherever a Clock reading appears; the judgement about what the reading means is always the reader's.
Data sources
Income: Singapore Department of Statistics table M810361 — median monthly household employment income among resident employed households, annual since 2000, published each February in "Key Household Income Trends". Prices: HDB resale transactions via data.gov.sg (granular dataset, 2017 onwards), from which PropKaki computes the medians. Both sources are re-ingested automatically, and every published figure states the year it refers to.
Version history
| Version | Date | Change |
|---|---|---|
| 1.0 | 12 June 2026 | First published definition. Gross-income years on matching years, 4-room headline plus all-types reading, year-end price annualisation (the underlying series have been published on the tracker since June 2026). |
Any future change to the formula or its inputs will be recorded here with a new version number and announced on the market data changelog. Numbers already published are never silently restated.
Citing the PropKaki Affordability Clock
Preferred citation:
The PropKaki Affordability Clock™ name and methodology are published by Straits Intelligence Pte. Ltd. (UEN 202615220E), operator of PropKaki. The underlying statistics belong to their issuing agencies. The computed series are free to reuse with attribution to "PropKaki (propkaki.sg)" under CC BY 4.0.
Current Clock readings, the income series and the explorer are on the Housing Affordability Tracker. Free JSON and CSV endpoints are listed in its "Use this data" section.