What’s the difference in depreciation between a 99y lease condo VS resale HDB?

The most comprehensive study (to my knowledge) is this NUS study done last year. They analyzed 500k HDB flats, 70k 99-year lease condos, and ~70k freehold condos.

• In the first 10 years, depreciation is across the 3 groups are very similar, though HDB flats depreciated just slightly more

• In the 10-30 years, depreciation for HDB and leasehold condos are quite similar - but freehold condos decrease much more slowly

• Beyond 30 years, HDB flats depreciate significantly more slowly than leasehold condos. The professor for the study cited the government's Home improvement program to regularly upgrade HDBs as likely the key reason for this.

Hence, from a purely depreciation perspective, a resale HDB would in general be a better a buy. Of course, this is on average; specific situations and units may vary.