Apartment rebuild dilemma in central Tokyo location – sell now, downsize, or pay extra to keep size? Advice needed

I own a 90m² apartment in a central Tokyo location. Bought in late 2019 for ¥80M, now estimated worth ~¥180-220M (mid ¥200M). Remaining mortgage ~¥55M on a sweet fixed loan (1% for 30 more years). Current total monthly cost ~¥238k.

The building (1970s vintage) is moving toward a possible rebuild. Vote pending, but if it goes ahead:

  • Option to keep similar size but pay ~¥170M top-up
  • OR downsize to ~60m² at no extra cost
  • Either way: 2-year evacuation period (extra ~¥15M in temp housing + moving while still paying mortgage)

My proportional land share is sizable and drives a lot of the value.

Options:

  1. Sell now
    Net cash: ~¥130-150M
    Rent 100m² apartment place nearby (~¥800k/mo)
    Invest the proceeds (leaning S&P 500)

  2. Downsize to 60m² (no extra payment)
    Ride out the 2 years, get a modern smaller unit, sell around 2028-2029 for ~¥150-180M → net ~¥135-155M cash then
    Rent + invest after

  3. Pay the ¥170M top-up to keep current size
    New loan ~¥225M total, payments jump to ~¥700-800k/mo
    Keep full size + land share in new building

Quick 20-year projections (S&P 10% return, Central Tokyo rent growing 5-7%/yr):

  • Option 1: ~¥550-650M net gain
  • Option 2: ~¥650-750M net gain (highest – gets rebuild uplift for free)
  • Option 3: ~¥300-450M equity gain in property (lowest)

Leaning toward Option 2 as the best bang for buck, but wondering what people who’ve been through Tokyo condo rebuilds think.

Any input? Thanks!

by Lunchisnice