Rebalancing bands vs. the calendar: the 5/25 rule with worked triggers

Calendar rebalancing — checking your allocation once a year and resetting it — is the advice most investors get, and it works. But it has a quiet flaw: it's blind to what markets do between checkups. A March crash can leave you underweight stocks for nine months before your December review notices, missing the rebalancing opportunity entirely. Band-based rebalancing fixes this by defining tolerance ranges around each target and acting only when an asset breaches its band. You trade less in calm years, more in volatile ones — which is exactly when rebalancing pays.

The 5/25 rule, precisely stated

The most widely used band system is Larry Swedroe's 5/25 rule. Each asset class rebalances when it drifts from target by the smaller of two limits: 5 absolute percentage points, or 25% of the target weight in relative terms. The absolute band governs large allocations; the relative band protects small ones, where 5 points of drift would be a huge proportional change. You use whichever band is tighter for that asset.

• A 40% allocation: absolute band is 35-45%; relative band is 30-50% (25% of 40 is 10 points). The absolute band is tighter, so it governs — act at 35% or 45%.
• A 10% allocation: absolute band is 5-15%; relative band is 7.5-12.5% (25% of 10 is 2.5 points). The relative band is tighter — act at 7.5% or 12.5%.
• The crossover sits at a 20% target weight, where both rules give the same ±5-point band. Above 20%, absolute governs; below, relative governs.

How often do bands actually trigger?

Less than people expect. Backtests of 5/25-style bands on stock/bond portfolios show roughly one to two triggers per year in volatile markets and sometimes none for two or three calm years running. That's the feature: bands concentrate your trades where they earn something. Historical comparisons of band vs. calendar rebalancing show similar long-run returns on average, but bands capture more of the 'rebalancing bonus' in high-volatility periods (2008-2009, 2020, 2022) — the periods that also test your discipline most.

The checking problem — and the honest fix

Bands have one practical weakness: someone has to notice the breach. Checking daily invites tinkering; never checking defeats the system. The clean solution is monthly monitoring with band-based action — look on the first of each month, act only if a band is breached. You'll catch any drift large enough to matter (breaches that appear and fully reverse within a month are rare and harmless to miss) while touching the portfolio at most twelve times a year and usually zero. Some brokerages and portfolio trackers will email you drift alerts, which removes even the monthly ritual.

Where to execute the trades

1. Tax-advantaged accounts first: sales inside an IRA or 401(k) have no tax consequence, so do the heavy lifting there even if the drift shows up portfolio-wide.
2. New contributions and dividends second: turn off automatic dividend reinvestment in taxable accounts and point the cash at underweight assets.
3. Taxable sales last: if you must sell in taxable, prefer lots with losses or the smallest gains, and mind the one-year line for long-term treatment.

Calendar, bands, or both?

The honest comparison: calendar rebalancing wins on simplicity and is nearly impossible to get wrong; bands win on responsiveness and trade efficiency. The hybrid most practitioners actually use is 'monthly look, band trigger, annual failsafe' — bands govern action, but a once-a-year full reset (on your birthday, in January, whenever) catches anything the bands tolerated. For a portfolio under roughly $50,000, skip all of it and just buy the laggard with contributions; drift is too small in dollar terms to outrank simplicity.

Choosing your own band width

The 5/25 numbers aren't sacred — they're a sensible middle setting on a dial you're allowed to turn. Tighter bands (say 3/15) keep risk closer to target but trigger more trades, more taxes, and more temptation to fiddle; looser bands (7/35) let winners run longer and suit taxable accounts where every sale has a cost. What matters far more than the exact width is that the bands are written down before markets move, applied to every asset the same way, and never widened mid-crash because selling bonds to buy falling stocks feels frightening. A band you renegotiate under stress isn't a system; it's a mood with a spreadsheet.

The bottom line

Rebalancing exists to control risk, and bands control it in real time instead of on an anniversary. Write down each asset's target and its 5/25 trigger points, glance at the portfolio monthly, act only on a breach, and route new money to laggards so most breaches never happen. It's ten minutes of setup and five minutes a month — and in the one year per decade when markets go haywire, it's the difference between a system that bought the panic and a calendar that slept through it.