Amortising Bond: When Your Principal Comes Back in Instalments, Not One Lump Sum
An amortising bond is a fixed income instrument that repays part of its principal along with each interest payment over the bond’s life, rather than returning the entire principal in a single lump sum at maturity — the opposite structure of a standard ‘bullet’ bond, which is what most Singapore Savings Bonds, T-bills, and typical corporate bonds use.
Not financial advice. All figures for educational reference only. Data as at August 2026. Last updated: August 2026.
Key Takeaways
- In an amortising bond, each periodic payment includes both an interest component and a partial principal repayment, so the outstanding principal balance — and therefore future interest amounts — steadily shrinks over the bond’s life.
- This contrasts with a bullet bond (the more common structure for Singapore Savings Bonds, T-bills, and most corporate bonds), where 100% of the principal is repaid only at maturity.
- Amortising structures are common in asset-backed securities, mortgage-backed securities, and project finance bonds, where the underlying cash flows (like loan repayments or project revenues) naturally arrive gradually rather than in one lump sum.
- Because principal is returned progressively, an amortising bond’s average life (weighted-average time to receive cash flows) is shorter than its stated final maturity date, which affects duration and interest rate sensitivity calculations.
- Amortising bonds reduce reinvestment concentration risk at maturity, since you’re not receiving one large principal sum all at once, but they also mean your capital isn’t fully working at the bond’s stated coupon rate for its entire term.
What Is Amortising Bond?
Most bonds retail Singapore investors are familiar with — Singapore Savings Bonds, Treasury bills, and typical corporate bonds — are ‘bullet’ bonds, meaning the issuer pays periodic interest but returns the entire face value of principal only once, at maturity. An amortising bond restructures this: instead of one large repayment at the end, principal comes back gradually, spread across the life of the bond alongside the interest payments. This structure mirrors how a mortgage or car loan works — each instalment payment includes both interest and a bit of principal — and for good reason: amortising bonds are frequently backed by pools of exactly these kinds of underlying loans, such as mortgage-backed securities (MBS) or asset-backed securities (ABS), where the bond’s own cash flow schedule is designed to match the cash flows coming in from the underlying loan pool.
How Does Amortising Bond Work in Singapore?
Consider a S$10,000 amortising bond with a 5-year term and an annual coupon rate applied to the declining balance. In year one, interest is calculated on the full S$10,000, plus a scheduled principal repayment reduces the outstanding balance — say to S$8,000. In year two, interest is now calculated on the smaller S$8,000 balance, plus another principal repayment further reduces it, and this pattern continues until the balance reaches zero by the final scheduled payment. Because the outstanding principal — and therefore the interest earned — declines each year, the bond’s total cash flow schedule looks quite different from a bullet bond of the same face value and coupon rate, even though both might carry an identical stated ‘coupon rate’ at issuance.
Amortising Bond Example
An investor holding a Singapore-listed amortising asset-backed security tied to a pool of auto loans receives declining periodic payments over the security’s life — larger combined interest-plus-principal payments early on, tapering as the underlying loan pool itself amortises down, until the security is fully repaid well before what might appear to be its final legal maturity date on paper.
Advantages of Amortising Bond
- Reduces concentration risk at maturity — instead of a single large repayment event, principal returns gradually, spreading out reinvestment decisions rather than facing them all at once.
- Cash flow matches underlying assets — for securities backed by loan pools, an amortising structure naturally mirrors how the underlying collateral itself generates cash, reducing structural mismatch.
- Shorter average life than stated maturity — because principal returns progressively, the bond’s effective duration is often shorter than its nominal term, which can appeal to investors wanting less long-duration interest rate exposure.
- Predictable declining balance — the repayment schedule is typically known upfront, making cash flow planning straightforward despite the more complex structure.
Risks and Limitations
- Reinvestment risk spread across the whole term, not eliminated — you still need to reinvest each principal instalment as it arrives, and if rates have fallen, you’re reinvesting smaller sums at potentially lower rates repeatedly rather than just once.
- More complex to evaluate — comparing an amortising bond’s true yield and duration against a simpler bullet bond requires understanding the full repayment schedule, not just the headline coupon rate.
- Prepayment risk in loan-backed structures — if the underlying loans (e.g. mortgages) are prepaid faster than expected, principal can return even sooner than scheduled, further complicating reinvestment planning.
- Less capital working at the coupon rate over time — because principal shrinks progressively, less of your original investment remains earning the stated coupon rate in later years compared to a bullet bond of the same size.
Amortising Bond vs Bullet Bond
The two structures differ fundamentally in how and when principal is returned to the investor.
| Aspect | A | B |
|---|---|---|
| Principal repayment | Gradually, alongside each interest payment | Entirely at maturity, as one lump sum |
| Interest calculation basis | Declining outstanding balance | Full face value throughout the term |
| Common examples | Mortgage-backed securities, project finance bonds | Singapore Savings Bonds, T-bills, most corporate bonds |
| Average life vs stated maturity | Shorter — principal returns before final maturity date | Equal — full principal only returns at the maturity date |
| Reinvestment pattern | Repeated, smaller reinvestment decisions over time | One large reinvestment decision at maturity |
The Bottom Line
An amortising bond spreads principal repayment across the life of the bond instead of concentrating it all at maturity like a typical Singapore Savings Bond or T-bill — a structure that mirrors underlying loan-based collateral well, but requires investors to evaluate the full repayment schedule, not just the headline coupon, to understand the true return and duration profile.