Yield to maturity for debt mutual funds

Yield to maturity (YTM) of a debt mutual fund is the weighted average internal rate of return (IRR) of all the bonds held in the portfolio, assuming each bond is held until maturity, all coupon payments are received on schedule, and all principal amounts are repaid in full. It represents the pre-expense annual return the portfolio is expected to generate, expressed as a percentage per annum. YTM is a forward-looking expected return estimate, not a historical return.

YTM is one of the three mandated risk disclosures for debt funds in India (alongside Macaulay duration and modified duration) and is the primary metric investors use to estimate the expected returns from a debt fund before choosing between categories.

YTM for a single bond: formula

For a bond with \(n\) coupon periods to maturity:

\[ P = \sum_{t=1}^{n} \frac{C}{(1+y)^t} + \frac{F}{(1+y)^n} \]

Where:

YTM is the rate \(y\) that equates the sum of discounted future cash flows with the current market price. It cannot be solved analytically in general, it requires iterative numerical methods (Newton-Raphson or financial calculator).

Portfolio YTM calculation

For a mutual fund portfolio, YTM is the weighted average of individual bond YTMs:

\[ \text{YTM}{\text{portfolio}} = \sum{i=1}^{n} w_i \times y_i \]

Where \(w_i\) is the market value weight of bond \(i\) and \(y_i\) is the YTM of bond \(i\).

This weighted average is an approximation, the true portfolio YTM is strictly the IRR of the entire portfolio’s cash flows, but the approximation is accurate enough for investor communication purposes and is the standard AMFI disclosure methodology.

What YTM tells the investor

For a debt fund investor:

• Expected return indication: The YTM minus TER gives a reasonable estimate of the fund’s net expected return if held for a period roughly equal to the portfolio’s Macaulay duration.
• Forward-looking, not backward: Unlike trailing 1-year or 3-year returns, YTM is a current estimate of future returns embedded in today’s bond prices.
• Not guaranteed: YTM assumes zero defaults (all coupons and principals received as contracted). If any bond in the portfolio defaults or is restructured (as with the Franklin Templeton credit fund collapse in 2020), actual returns will be lower.

Typical YTM ranges in Indian debt funds (2024–25)

With the RBI repo rate at 6.50 per cent and 10-year G-sec yield around 7.10 per cent:

Credit risk funds show higher YTMs because they hold lower-rated bonds (AA, A, BBB) that pay higher coupons to compensate for default risk. The higher YTM is not a “free lunch”, it comes with higher default probability and NAV volatility during credit stress events.

YTM and credit quality interaction

The relationship between YTM and credit quality is fundamental:

\[ y_{\text{bond}} = y_{\text{G-sec}} + \text{Credit spread} \]

Where the credit spread is the additional yield demanded by investors to compensate for default risk above the government’s risk-free rate. Typical spreads (2024–25):

A fund with a high YTM relative to peers holding the same maturity bucket is likely holding lower-rated (riskier) bonds. Investors should not choose a debt fund solely by YTM without examining the credit quality distribution.

YTM vs trailing returns: the key difference

Many investors confuse YTM with historical returns:

In a rising rate environment, a fund’s trailing 1-year return will be low (or negative) even as its YTM rises (because bond prices fall when yields rise). The high YTM then becomes the estimate of future return once the rate cycle normalises. Conversely, in a falling rate environment, trailing returns are high because bond prices have risen, but YTM falls, indicating lower future return potential.

YTM and the TER drag

Net expected return for the investor:

\[ \text{Expected net return} \approx \text{Portfolio YTM} - \text{TER} \]

For a liquid fund with YTM of 6.65% and direct plan TER of 0.10%: expected net return ≈ 6.55%.

For a medium duration fund with YTM of 7.30% and direct plan TER of 0.35%: expected net return ≈ 6.95%.

This simple approximation holds if the portfolio is held static. In practice, as bonds mature and new bonds are added at prevailing yields, the portfolio YTM changes continuously.

Roll-down return (YTM plus capital gain from ageing)

For investors holding a fund for a period shorter than the fund’s duration, additional return comes from “rolling down the yield curve”, as bonds age, they move to shorter maturities where yields are typically lower (in a normal upward-sloping yield curve), causing their prices to rise. The total return is approximately:

\[ \text{Total return} \approx \text{YTM} + \text{Roll-down return} \]

Roll-down return can be material for short duration funds (1–3 years) in a steepening yield curve environment.

YTM disclosure and AMFI standards

SEBI and AMFI mandate that all debt fund monthly factsheets disclose the portfolio YTM as of the last business day of the month. AMCs must also disclose whether the YTM is computed gross (before TER) or net, the standard is gross YTM (pre-expense). Investors should subtract the fund’s TER to estimate net expected return.

See also

• Macaulay duration in debt funds
• Modified duration in debt funds
• Credit quality bucketisation in debt funds
• Total expense ratio in mutual funds
• Rolling vs trailing returns
• Mutual fund
• SEBI

References

1. Fabozzi, F. J., Fixed Income Mathematics, 4th edition, McGraw-Hill.
2. SEBI circular SEBI/HO/IMD/DF3/CIR/P/2017/114 dated 6 October 2017, debt fund categories.
3. AMFI, YTM disclosure guidelines for debt fund factsheets, amfiindia.com.
4. RBI, Government Securities Market Primer.
5. CRISIL, Debt fund analytics and YTM data, crisil.com.