By The Address desk · Last verified 7 October 2026
Besides BTO, HDB sells new flats in two other ways. The Sale of Balance Flats (SBF) offers flats left over from earlier BTO exercises, surplus SERS replacement flats and flats HDB has bought back, many of them under construction, near completion or already completed. You apply in a sales exercise and HDB ballots applicants, with the same ballot chances as BTO. Flats still unselected after SBF go to Open Booking: you apply online, get a queue number, and book on a first-come, first-served basis, sometimes as early as the next working day. Both need a valid HDB Flat Eligibility (HFE) letter first.
If you need a home sooner than a BTO wait allows, these two routes are worth knowing well. They reward buyers who are prepared and flexible.
Quick facts
- SBF flats come from earlier BTO exercises, surplus SERS replacement flats and repurchased flats.
- SBF can include Community Care Apartments, 2-room Flexi, 3-, 4-, 5-room, Executive and 3Gen flats.
- SBF ballot chances match BTO: 3 for first-timer parents and married couples, 2 for other first-timer families, 1 for second-timer families and first-timer singles.
- Unlike BTO, SBF gives no extra ballot chances after unsuccessful attempts.
- Open Booking offers unselected flats from past SBF exercises, allocated by queue number rather than ballot.
- HDB launched 9,012 flats across its February 2026 BTO and SBF exercises.
BTO, SBF and Open Booking compared
| Point | BTO | Sale of Balance Flats | Open Booking |
|---|---|---|---|
| Which flats | New projects not yet built | Balance, surplus SERS and repurchased flats | Flats left unselected after past SBF exercises |
| Flat status | To be built | Under construction, near completion or completed | Mixed; often completed or near completion |
| How flats are allocated | Computer ballot | Computer ballot | Queue number, first come, first served |
| When you can apply | During a sales exercise | During an SBF exercise | Whenever applications are open |
| Extra ballot chances | Yes, for repeated Standard flat attempts by first-timer families | No | Not applicable |
| Choice of flats | Wide within a project | Limited and scattered across towns | Whatever remains, often limited |
How Open Booking works, step by step
- Get your HFE letter on the HDB Flat Portal. It confirms your eligibility, grants and loan, and can take about a month, longer in peak periods.
- Browse the flats available on the HDB Flat Portal, with their towns, floor levels and expected completion.
- Apply online for your chosen flat type and receive a queue number straight away.
- Attend your booking appointment, which can be as early as the next working day, where possible.
- Book a flat that is still available when your turn comes, and pay what is due at booking.
HDB suspends Open Booking applications when all the flats are booked, and before each injection of fresh supply, so the list changes through the year. Check the portal often.
Who does well with SBF and Open Booking?
| Your situation | Why these routes help |
|---|---|
| You need a home within a year or two | Completed or nearly completed flats can mean much earlier keys than a new BTO |
| You are flexible on town and floor | Choice is limited, so flexibility turns leftovers into options |
| You want a new flat but missed BTO ballots | Open Booking skips the ballot entirely |
| You want subsidies and grants | Eligible buyers receive HDB grants for SBF and Open Booking flats as for other new flats |
The WahLiao Verdict
If time matters more than picking the perfect stack, SBF and Open Booking are the smartest doors HDB offers. Get your HFE letter ready before you need it, keep a short list of acceptable towns and flat types, and check the portal regularly. When a suitable flat appears in Open Booking, move quickly: the queue rewards the prepared, and a good flat with early keys is often worth more than a slightly better one years away.
Questions people ask
Why are some flats left over?
Some buyers cancel bookings, some flats are returned to HDB, and some units are less popular, such as those on low floors or facing certain directions. They are not necessarily worse homes.
Do I need an HFE letter for Open Booking?
Yes. As with BTO and SBF, you need a valid HFE letter before you apply, so apply for it early.
Can singles use SBF and Open Booking?
Yes, if they meet HDB’s eligibility rules for singles and the flat type is one they may buy. First-timer singles get one ballot chance in SBF.
What if I am invited but do not book?
Declining a chance to book can affect your priority in later exercises under HDB’s non-selection rules. Read the rules on the HDB Flat Portal before you apply.
Sources: HDB, modes of sale: BTO, SBF and Open Booking, February 2026 BTO and SBF launch and process for buying a new flat. The Address explains; it does not advise.
Read next: How a BTO Application Works: The HFE Letter, the Ballot and Booking a Flat · HDB Housing Grants: The Enhanced Grant, the Family Grant and the Proximity Grant · Back to The Address
For what’s worth it this week, with the bill shown, read The WahLiao Week.
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