I have a spreadsheet that tells me exactly which positions are off-target by how many dollars. It took thirty minutes to build and it works — but I still have to log into my brokerage, click through the trade ticket, and hope I did not fat-finger a decimal. The gap between knowing what to rebalance and actually doing it is where most portfolios drift.
I tested five rebalancing approaches over the past year: Google Sheets with GOOGLEFINANCE, dedicated platforms (Passiv and Portseido), brokerage built-in tools (M1 Finance and Fidelity Basket Portfolios), and a minimal Python pipeline. This article covers what each approach does well, where it falls short, and the decisions that matter more than tool choice — specifically, your rebalancing threshold, tax awareness, and how often you actually follow through.
Threshold Versus Calendar Rebalancing
Before evaluating tools, the decision framework matters. Calendar rebalancing trades on a fixed schedule — quarterly, annually — and the calendar decides for you. It is simple, but between dates your allocation can drift substantially during fast markets, and you may execute trades when drift is minor, generating transaction costs for barely meaningful adjustments.
Threshold rebalancing triggers a trade only when an asset class deviates from its target by a set percentage — a common rule is ±5% absolute. Fewer trades in quiet markets, faster correction during sharp moves. The trade-off is behavioral: you need to monitor frequently enough to catch breaches.
I use a hybrid: check monthly, trade only when something crosses a 5% absolute band. This gives me the emotional containment of a schedule with the cost-efficiency of a threshold.
If you rebalance more frequently than quarterly, ask whether the trades are correcting drift or chasing recent performance. Studies by Vanguard and Morningstar suggest the difference in long-term returns between quarterly and annual rebalancing is negligible for a standard stock-bond portfolio. More frequent rebalancing is usually more trading, not more alpha.
The Five Approaches I Tested
Google Sheets with GOOGLEFINANCE is where most hands-on investors should start. A five-column table — ticker, target weight, current shares, current price, current value — plus formulas for allocation percentages and dollar deviations, gives you a minimum viable rebalancing dashboard. =GOOGLEFINANCE("VTI", "price") pulls live prices for each holding. The limitation is execution: Google Sheets cannot place trades. It also occasionally returns stale data for mutual funds, and error handling is brittle — IFERROR wrappers are mandatory. For a five-to-ten ETF portfolio, this approach is free, transparent, and takes under an hour.
Passiv integrates directly with Interactive Brokers and Questrade. You define a target portfolio, Passiv tracks drift, and with a paid subscription (~$99 USD/year) it generates and places rebalancing trades through the brokerage API — as close to one-click rebalancing as I have found. The catch: US investors using Fidelity, Schwab, or Vanguard cannot use it. The brokerage integration is the product; without it, Passiv is just another tracker.
Portseido is an analytics platform first, rebalancing tool second. It supports manual entry and CSV imports rather than live brokerage links — less automation, broader coverage. The analytics layer visualizes drift over time and surfaces correlation between holdings that a spreadsheet misses. ~$14/month for the full feature set. For a portfolio under $100,000, the subscription cost as a percentage of assets is worth calculating — $99/year is 0.1% of a $100,000 portfolio, more than many ETF expense ratios.
M1 Finance builds rebalancing into the account structure. Define a target allocation "pie," and every deposit flows to the most underweight slice automatically. There is a manual rebalance button that executes all buy and sell orders at once. The limitations: US-listed stocks and ETFs only, FIFO tax-lot selection, a single daily trading window, and no visibility into holdings at other brokers. If M1 holds your whole portfolio, it is the simplest rebalancing experience available.
Fidelity Basket Portfolios offers similar functionality with the advantage of living inside a full-service brokerage — your baskets sit alongside your regular account and IRA. The disadvantage: $50,000 minimum balance and $4.99/month, which is hard to justify when M1 does the same thing for free.
DIY Python gave me total control at the cost of total responsibility. I built a minimal pipeline — yfinance for price data, a CSV for holdings, ~80 lines that compute drift and output trades with dollar amounts and share counts. I do not automate trade execution. The script computes, I review, I manually place. This eliminates arithmetic errors without adding the complexity of brokerage API integration, authentication, and order validation. I run it the first Saturday of each month and place the flagged trades in under ten minutes.
Tax-aware rebalancing — selling highest-cost-basis shares first, deferring gains, or concentrating rebalancing in tax-advantaged accounts — requires information most tools cannot see. A spreadsheet does not know which lot has the lowest embedded gain. A tracker linked to your brokerage might know, but it probably will not optimize across taxable and tax-advantaged accounts simultaneously. Rebalance in tax-advantaged accounts whenever possible, and let taxable positions drift within wider bands before triggering a sale.
A Workflow You Can Build in an Afternoon
Here is the pipeline I landed on. It acknowledges that the real bottleneck is not trade execution — it is the moment where you stare at the numbers and second-guess the target allocation you set six months ago.
Step 1: Define your target once. Write it in a CSV — ticker, target weight, account location — and never modify it except during a planned annual review. If you rebalance against a moving target, you are market timing with more steps.
Step 2: Pull current prices. yfinance or alpaca-py handles this in three lines. For spreadsheet users, GOOGLEFINANCE. Pull from the same source consistently — switching feeds introduces noise into the drift calculation.
Step 3: Compute drift. Subtract target weight from current weight. Flag any position where absolute deviation exceeds your band.
Step 4: Generate trades. For each flagged position: (target_weight × total_value) − current_value. Convert to shares by dividing by current price.
Step 5: Place trades. If you use M1 or Fidelity, this is one click. Otherwise, log in and type. Accept this as the point where human review adds value — you catch the mistaken ticker or the position that drifted for a reason you forgot about.
Step 6: Verify. After settlement, re-run the script and confirm every position is within its band. If something is still off, check whether a fund distribution hit between the trade date and settlement.
I run this monthly but trade two to four times per year. The rest of the time, checking takes five minutes and confirms that nothing needs doing.
The Hidden Cost of Over-Rebalancing
Tracking error — how far your portfolio deviates from its benchmark — has a U-shaped relationship with rebalancing frequency. If you never rebalance, drift accumulates. If you rebalance too aggressively, you incur transaction costs, short-term capital gains, and in a trending market you are systematically selling winners to buy laggards — a headwind to returns.
The sweet spot is wider than most investors assume. A 2021 study in the Journal of Portfolio Management found that rebalancing at a 10% absolute threshold versus 5% produced nearly identical risk-adjusted returns over 30 years, with materially fewer trades. The precision of your threshold matters far less than the consistency of your execution. A spreadsheet you actually use beats an automated tool you ignore.
This article describes tools and methods I have personally tested. It is not investment advice, and no allocation rule or rebalancing frequency discussed here should be interpreted as a recommendation for any specific portfolio. Tax treatment varies by jurisdiction and individual circumstances. Consult a qualified professional before making decisions that affect your financial plan.
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