How to build a portfolio

Allocation, diversification, and rebalancing.

TL;DR

Building a portfolio means deciding what to own (allocation), in what proportions, and how to maintain those proportions over time (rebalancing). The two questions that matter: time horizon and risk tolerance.

Core principles

Decades of academic research point to a handful of rules that beat nearly all active managers.

→Diversify — don't concentrate in one stock, sector, or country.
→Keep costs low — every 1% in fees compounds to 30%+ over 30 years.
→Match assets to time horizon — stocks for the long term, bonds and cash for near-term needs.
→Rebalance periodically — restore target allocations when one part drifts.

Allocation templates

Three battle-tested starting points.

→60/40 — 60% stocks (VOO/VTI) + 40% bonds (BND/AGG). The classic balanced portfolio.
→Three-fund — US stocks + international stocks + bonds. Bogle's recommendation.
→Lifecycle / target-date — automatically becomes more conservative as retirement approaches.

Rebalancing rules

Pick one and stick with it: annually on a fixed date, when any allocation drifts more than 5pp, or every quarter. Emotion is the enemy.

Worked example

Three-fund portfolio for $50,000

30 years old, retirement at 65 — long horizon, can tolerate volatility.

1Allocation70% US / 20% international / 10% bonds
2VOO (US)$35,000
3VXUS (international)$10,000
4BND (bonds)$5,000
5Annual rebalanceBring back to target if drift > 5pp
6Annual costCombined expense ~0.05% = $25/yr on $50K

Takeaway

Three ETFs, $25/yr in fees, globally diversified. Most active managers don't beat this consistently after fees.

Common mistakes

What to avoid

!Chasing performance — buying last year's winner that's already up 100%
!Over-concentrating in employer stock or one sector you 'understand'
!Trading too often — costs and taxes compound quickly
!Forgetting rebalancing — gains accumulate, risk profile drifts

Self-check

Test yourself

Q1What does rebalancing do mechanically?+

Sells what's grown faster than your target and buys what's lagged — 'buy low, sell high' on autopilot.

Q2Why does a 1% annual fee matter so much over 30 years?+

Compounded over decades, 1% in fees can eat 25–30% of your final balance.

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