SUB vs ZMUN

SUBAiShares Short-Term National Muni Bond ETF

ZMUNCF/m Ultrashort Tax-Free Municipal ETF

In short

SUB Munis, but only the near end of the curve. Since 2008 SUB has tracked an AMT-free index of investment-grade municipal bonds maturing inside five years, paying tax-exempt income monthly with far less rate sensitivity than long-dated muni funds.

ZMUN The first ETF built purely on callable munis, tracking an index F/m co-developed with Bloomberg. It buys investment-grade tax-exempt bonds already callable or callable within three months, which keeps the maturity clock very short.

Stated mandate

SUB The fund seeks to track an index of short-term, investment-grade U.S. municipal bonds maturing from one month through five years, providing tax-exempt income while managing interest-rate risk.

ZMUN The fund seeks to track, before fees and expenses, the price and yield performance of the Bloomberg Municipal Bond Currently Callable Index. It uses a passive representative-sampling approach focused on U.S. tax-exempt investment-grade municipal bonds that are currently callable or callable within three months.

Why people hold it

• SUB Charges 0.07% a year against a category median near 0.30%. On tax-exempt bond income, that fee gap is a meaningful slice of what actually reaches you.
• Two dials set on purpose: maturities from one month to five years, and an AMT-free index, so neither rate swings nor the alternative minimum tax hit the same way.ishares.com
• A multi-billion-dollar fund running since 2008 under iShares, with tight tracking of its ICE benchmark. One of the sturdier implementations in the muni group.
• Pays monthly, so the tax-exempt income arrives on a regular cadence rather than in quarterly lumps.

• ZMUN A corner of the muni market nobody else had packaged: F/m calls it the first ETF dedicated to callable municipal bonds, on an index built with Bloomberg.fminvest.com
• The mechanism is the point: bonds callable now or within three months act like ultrashort paper, so price moves from rate swings tend to be muted.
• Interest is exempt from federal tax and, for some holders, certain state taxes. Spread across roughly 170 investment-grade issues, with cash paid monthly.
• No style drift: it is a passive representative-sampling fund, and the portfolio it holds matches the mandate written in its prospectus.

Worth knowing

• SUB The five-year ceiling is the whole design, and it cuts both ways: less rate sensitivity, but a shorter stretch of the curve to draw income from than full-maturity muni funds.
• This is a national portfolio. Single-state funds like NYF chase a home-state tax break that a nationwide muni basket cannot offer.
• Broad-maturity peers VTEB and SCMB run at 0.03%. The short-end tilt here costs a few basis points more.

• ZMUN 0.30% a year sits above the short-muni group's 0.25% median, and far above the index giants VTES (0.05%) and SUB (0.07%).
• Callability cuts both ways: issuers can redeem these bonds at their option, capping price upside and forcing reinvestment at whatever rates exist that day.fminvest.com
• A 2025 launch that is still small and thinly traded. Short track record, and limit orders are the sane way in and out.

Full SUB profile⁠

Full ZMUN profile⁠