Medium Duration Debt Fund: What SEBI’s 3-4 Year Band Really Means

A medium duration debt fund sounds like the most forgettable corner of a mutual fund app. No glamour, no ten-bagger stories. Yet this is the category where a lot of conservative money quietly sits, and where a single rate move can show up in your NAV faster than most investors expect. The rule that defines it is short: SEBI wants the portfolio’s Macaulay duration between 3 and 4 years. Everything else about how the fund behaves flows from that one band.

Let’s unpack what the band means, what the fund manager is allowed to do outside it, and how you can estimate the hit (or the gain) from a rate move with nothing more than a calculator.

What SEBI says a medium duration debt fund must hold

SEBI first drew up the debt fund categories in its October 6, 2017 circular on categorisation and rationalisation of schemes. Category 7 there was named “Medium Duration Fund”: investment in debt and money market instruments such that the Macaulay duration of the portfolio is between 3 and 4 years.

The current rulebook is the SEBI Master Circular for Mutual Funds dated March 20, 2026. In its debt scheme table the same slot appears as “Medium Term Fund”, and the definition has not moved: Macaulay duration of the portfolio between 3 years and 4 years. So if your fund house still calls it “medium duration” and a newer document says “medium term”, they are describing the same 3-4 year band. We’ll use both names here, because investors search for both.

The neighbours in that table help put it in context. Per the 2026 master circular:

• Short Term Fund: Macaulay duration of 1 to 3 years.
• Medium Term Fund: 3 to 4 years.
• Medium to Long Term Fund: 4 to 7 years.
• Long Term Fund: greater than 7 years.

Notice what is missing. There’s no rule here about credit quality. A medium duration fund can hold government securities, top-rated PSU bonds or lower-rated corporate paper. The category tells you about interest rate sensitivity, not about default risk. That second dimension you have to check separately, which we’ll get to.

Macaulay duration in plain words

Macaulay duration is the present-value-weighted average time until you receive a bond’s cash flows. That’s the definition Wikipedia’s bond duration article gives, and it’s the cleanest way to think of it. A zero-coupon bond that pays only at maturity has a Macaulay duration equal to its maturity. A bond paying regular coupons has a duration shorter than its maturity, because some money comes back early.

For a fund, SEBI is specific about how to measure it. The master circular says Macaulay duration at the scheme level is the weighted average of the Macaulay duration of each instrument in the portfolio, with weights based on each holding’s proportion of AUM. It also says the duration is to be mentioned at portfolio level, not bond by bond.

Worked example 1: is this portfolio inside the band?

Take a hypothetical fund with three buckets of holdings:

The portfolio comes out at 3.65 years, comfortably inside 3-4. Interesting point: Bucket C on its own would sit in the medium-to-long band, and Bucket A would sit in the short-term band. Neither matters on its own. Only the blended number has to obey the rule. So a medium duration fund can, and often does, hold paper well outside 3-4 years.

The 3-4 year band is a rule about the whole portfolio’s average, not about any single bond. Two funds in the same category can hold very different paper and still both comply.

How much does the NAV move when yields change?

Duration earns its keep here. The link between Macaulay duration and price sensitivity is modified duration. Per the Wikipedia article, modified duration equals Macaulay duration divided by (1 + y/m), where y is the yield to maturity and m is the number of compounding periods a year. And for a small change in yield, the percentage change in price is approximately minus modified duration times the change in yield.

If yield to maturity is a new idea, our explainer on yield to maturity covers it with examples.

Worked example 2: a rate rise and a rate fall

Stick with our 3.65-year portfolio and assume a hypothetical portfolio yield of 7% with annual compounding (m = 1).

• Modified duration = 3.65 / 1.07 = about 3.41.
• If yields rise by 0.50 percentage point: price change is roughly minus 3.41 times 0.005, or about minus 1.71%.
• If yields fall by 0.75 percentage point: price change is roughly plus 3.41 times 0.0075, or about plus 2.56%.

On a hypothetical holding of ₹5,00,000, that’s a mark-to-market dip of roughly ₹8,528 in the first case and a gain of roughly ₹12,792 in the second. These are first-order estimates. The Wikipedia article notes that duration-based estimates work best for small, parallel shifts in the yield curve, so for bigger moves the real number will drift from this.

Worked example 3: same rate move, three categories

Now compare a 1 percentage point rise in yields across three hypothetical portfolios, each at a 7% yield with annual compounding:

That’s the trade-off in one table. The medium bucket sits in the middle: more rate risk than a short term fund, a good deal less than the 4-7 year category. If you’ve been burnt by a long bond fund in a rising-rate year, this is the gentler version, not a risk-free one.

The escape hatch: the “anticipated adverse situation” clause

Here’s a detail many investors miss. The 2026 master circular says that for the Medium Term Fund, portfolio Macaulay duration under an anticipated adverse situation is 1 year to 4 years. In other words, the fund manager may cut duration all the way down to one year if they expect rates to move against the portfolio.

It isn’t a free pass. The circular says that whenever duration is taken below the 3-year floor, the AMC has to record the reasons with adequate justification and keep them for inspection. Those written justifications go before the trustees at their next meeting, and the trustees review the portfolio and report it in their half-yearly trustee report to SEBI. The AMC also has to state its asset allocation under such an adverse situation in the scheme information document.

Worked example 4: what the defensive cut buys you

Say the manager in our example expects yields to rise and drops duration from 3.65 years to 1.5 years, still at a 7% yield. Modified duration falls to 1.5 / 1.07, about 1.40. A 0.50 percentage point rise in yields now costs roughly 0.70% instead of 1.71%. That’s the protection. The flip side: if the manager is wrong and yields fall, the fund gains far less than a fully invested 3-4 year portfolio would. So two medium duration funds can deliver very different returns in the same year purely because one manager used this clause and the other didn’t.

The adverse-situation clause turns a medium duration fund into a partly active rate call. Read the factsheet’s current duration, not just the category name.

Accrual versus price: how big a rate move eats a year’s income?

A debt fund’s return has two parts: the interest the bonds accrue, and the change in their prices. A handy rough check is how much yields must rise in a year to cancel that year’s accrual.

Worked example 5: the break-even yield move

With our hypothetical 7% portfolio yield and modified duration of 3.41, the break-even rise is roughly 7% divided by 3.41, or about 2.05 percentage points. In plain terms: on these assumptions, yields would need to climb by around two percentage points within the year before the price loss wipes out a full year of interest. For the 5.5-year portfolio in the earlier table, the same maths gives 7% / 5.14, or roughly 1.36 percentage points. For the 2-year portfolio, roughly 3.75 percentage points.

This is a back-of-the-envelope tool. It ignores convexity, expenses and the way the portfolio itself changes over a year. But it gives a feel for how much cushion each category carries.

Credit risk is a separate question

Since the category is defined only by duration, you need a second lens for credit. SEBI provides one through the Potential Risk Class (PRC) matrix. The master circular says every debt scheme is placed in one of nine cells, based on maximum interest rate risk (measured by Macaulay duration) and maximum credit risk (measured by a Credit Risk Value).

The interest rate classes are: Class I, Macaulay duration up to 1 year; Class II, up to 3 years; Class III, any Macaulay duration. A fund whose normal band is 3-4 years has to be able to go above 3 years, so in practice a medium duration fund sits in Class III on the rate axis. On the credit axis, Class A requires a Credit Risk Value of 12 or more, Class B 10 or more, and Class C below 10. In the circular’s credit table, G-Secs, AAA, SDLs and TREPS score 1, AA+ scores 2, AA scores 3, and so on down to unrated at 11 and below investment grade at 12.

Separately, the risk-o-meter method in the circular’s annexures gives a portfolio with Macaulay duration above 3 and up to 4 years an interest rate risk value of 5, on a scale where anything above 4 years gets 6. Our guide to the mutual fund riskometer explains how these scores feed the final label. If a medium duration fund is reaching for yield through lower-rated paper, that shows up in its PRC cell and riskometer. Our piece on the credit risk fund category shows what that kind of portfolio looks like when credit is the main bet.

How it compares with a dynamic bond fund

A dynamic bond fund, per the same SEBI table, invests across duration with no band at all. The medium duration fund gives the manager a much narrower box: 3-4 years normally, down to 1 year only under the documented adverse-situation route. If you want a fund house to make the full rate call for you, look at our dynamic bond fund explainer. If you want a predictable slice of rate exposure, the medium bucket is easier to reason about.

One more structural point. The master circular allows only one scheme per category per mutual fund, with exceptions for index funds and ETFs, fund of funds and sectoral or thematic funds. So each AMC will have at most one medium duration fund, which makes comparing across fund houses fairly straightforward.

A quick checklist before you buy one

1. Check the current portfolio Macaulay duration in the latest factsheet. Is it inside 3-4 years, or has the manager used the adverse-situation clause?
2. Check the PRC cell. A Class A or B fund on the credit axis is a very different animal from a Class C one.
3. Look at the yield to maturity alongside the credit mix. A noticeably higher yield than peers usually means more credit risk, not free money.
4. Run the duration maths for a 0.5 and 1 percentage point move against your own holding size, so a bad quarter doesn’t surprise you.
5. Match the holding period to the duration. Money you need in six months probably doesn’t belong in a 3-4 year duration portfolio.

For a broader framework on sizing risk across your money, our guide on risk management is a good companion read.

Sources

• SEBI: Master Circular for Mutual Funds, March 20, 2026
• SEBI: Categorization and Rationalization of Mutual Fund Schemes, October 6, 2017
• Wikipedia: Bond duration

Disclaimer: This article is for education only and is not investment advice. All portfolios, yields and amounts in the worked examples are hypothetical. Mutual fund investments are subject to market risks; read all scheme-related documents carefully and consult a SEBI-registered investment adviser before making any investment decision.