Enter what you hold and what you want to hold — the tool tells you exactly which positions are off target and what to buy or sell to fix it.
You set 60% US stocks two years ago, felt responsible about it, and never touched it again. One good equity run later you are quietly sitting at 68% — carrying more drawdown risk than you ever chose, and you would never know until the next correction reminded you. This tool makes that drift visible in one screen: enter your current holding values and your targets, set a drift threshold, and see exactly which asset classes are overweight, which are underweight, and by how much.
The default holdings include US Stocks, International Stocks, Bonds, and REITs — a common four-asset framework — but you can edit the names, values, and targets to match your actual portfolio. The rebalancing output shows you the specific buy and sell amounts needed to return to your target allocation, without requiring a spreadsheet or a financial advisor.
How portfolio drift actually happens — and why it compounds
Every asset class grows at a different rate. A year in which US equities return 18% while bonds return 4% leaves your equity allocation materially higher than your original target even if you never made a deliberate change. That drift is not inherently bad — you benefited from the run-up — but it changes your risk profile in ways you may not have intended.
The Drift Alert Threshold input lets you define how far any single holding can move from its target before a flag triggers. Setting it at 5% means a US Stocks target of 60% will flag if actual allocation reaches 65% or falls to 55%. The threshold is a personal risk tolerance decision: conservative investors often set it at 3–4%; investors comfortable with more tactical variation might use 7–10%.
The compounding problem with unchecked drift is that it tends to push portfolios toward whichever asset class has been outperforming recently — the opposite of the buy-low discipline most long-term strategies intend. A portfolio that started at 60/20/15/5 and drifted to 72/14/10/4 over three years of equity outperformance is now more exposed to equity drawdowns than the investor originally chose.
Reading the rebalancing output: what to buy and what to sell
The tool calculates the difference between your current holding value and the target value for each asset class at your current total portfolio size. If your portfolio is $112,000 and your US Stocks holding is $76,160 (68%) against a 60% target ($67,200), the tool tells you to sell $8,960 of US Stocks. The corresponding underweight classes get corresponding buy instructions.
This output is a starting point, not a trade order. Before executing, consider the tax implications of selling appreciated positions in taxable accounts, transaction costs, and whether a contribution-based rebalancing approach (directing new money toward underweight classes rather than selling overweight ones) is available to you. The tool gives you the math; the execution strategy depends on your account types and tax situation.
For investors with both taxable and tax-advantaged accounts, the most efficient rebalancing often starts in the tax-advantaged account — selling in a 401k or IRA generates no immediate taxable event. Once the tax-advantaged accounts are realigned, assess whether the taxable account still needs adjustment. The tool models your total portfolio as one pool; splitting the logic by account type is an execution refinement.
The drift threshold: choosing a number that works for you
A common question is how often to check and rebalance. The answer depends heavily on your threshold setting. With a 5% threshold, a low-volatility period might pass months without triggering. A volatile quarter might trigger in weeks. Setting the threshold at 2% means you are rebalancing frequently, which may incur more transaction costs than the precision is worth. Setting it at 10% means significant risk exposure changes can accumulate before you act.
Academic research on rebalancing suggests that annual calendar rebalancing and threshold-based rebalancing produce similar long-term outcomes, with threshold approaches generating modestly higher after-cost returns in volatile markets. The key variable is actually executing when the threshold is hit rather than letting drift run indefinitely. This tool makes the trigger visible — the discipline is yours to execute.
Customizing holdings beyond the four defaults
The tool ships with US Stocks ($68,000, 60% target), International Stocks ($22,000, 20%), Bonds ($15,000, 15%), and REITs ($7,000, 5%) as default holdings — a starting point that totals $112,000 and 100% in target allocations. You can change every name, value, and target to match your actual holdings.
Investors with more granular portfolios might track small-cap separately from large-cap, or split international into developed and emerging markets. The logic works the same: enter current value and target percentage for each row, set your drift threshold, and the tool calculates overweight and underweight positions for any number of asset classes. Targets must sum to 100% for the model to balance correctly.
This tool is for investors who want to think in allocation terms rather than individual security terms. If your portfolio is primarily individual stocks, the asset class framework may not apply cleanly. But for anyone using ETFs, index funds, or broadly diversified funds across categories, the allocation model is how professional portfolio managers think about balance and risk.
Rebalancing as a discipline, not an event
The investors who rebalance consistently tend to do so not because they are market-timing but because they have committed to a risk profile and want to stay inside it. Setting a drift threshold and checking it every quarter is a 15-minute discipline that keeps a long-term portfolio aligned with its original intent through any market environment.
This tool removes the friction from that check. Instead of pulling up multiple brokerage accounts, manually calculating percentages, and building a spreadsheet, you enter your current values and read the result in under a minute. Enter your current values, read the drift report, and save it — free, no card required. Checking it quarterly takes under a minute, which is exactly the kind of friction-free routine that actually sticks.
How to use it
- Review the default holdings (US Stocks, International Stocks, Bonds, REITs) and edit the names, current values, and target percentages to match your actual portfolio.
- Ensure your target percentages sum to 100% across all holdings.
- Set the Drift Alert Threshold (%) to define how far any position can drift before it flags — 5% is a common starting point.
- Read the drift status for each holding: which are overweight, which are underweight, and by how much.
- Follow the buy and sell amounts generated to return each holding to its target allocation at current portfolio size.
Who it's for
- Passive index investor doing a quarterly check — Updates three fund values after a strong equity quarter to see whether the 60/20/15/5 target has drifted above the 5% threshold and whether a rebalancing trade is needed.
- Pre-retiree shifting to a more conservative allocation — Changes target percentages from 70/15/10/5 to 50/15/30/5 to model the trades needed to execute a glide path adjustment over the next two years.
- New investor setting an initial allocation — Enters equal current values across four asset classes and sets targets to match a recommended three-fund portfolio, using the tool to confirm the math before making initial purchases.
- Investor using new contributions to rebalance — Checks which asset classes are underweight before directing a quarterly 401k rollover, targeting the buy amounts suggested by the tool rather than splitting contributions equally.
- Financial planning client reviewing with an advisor — Brings printed output showing current values and target drift to an annual review meeting instead of reconstructing the numbers from multiple statements.
Key terms
- Portfolio drift
- The gradual deviation of a portfolio's actual asset allocation from its target allocation, caused by different growth rates across asset classes.
- Drift alert threshold
- The maximum allowable deviation from a target allocation before a rebalancing review is triggered.
- Target allocation
- The intended percentage of a portfolio held in each asset class, representing the investor's chosen balance of risk and return.
- Rebalancing
- The process of buying and selling holdings to return a portfolio to its target allocation after drift has occurred.
Frequently asked questions
What drift threshold percentage should I use?
Most practitioners use 5% as a starting point — simple, easy to track, and not so tight that you are trading constantly. If you are in an accumulation phase with monthly contributions, a 7–10% threshold is reasonable because contributions can absorb drift. If you are in distribution or drawdown, 3–5% helps maintain a more consistent risk profile.
Does rebalancing improve long-term returns?
The evidence is mixed on return improvement, but the stronger case for rebalancing is risk management rather than return enhancement. Rebalancing keeps your portfolio inside the risk parameters you chose when you set your allocation. Without it, a long bull market in any asset class progressively increases your exposure to that class beyond what you intended.
How do I handle target percentages that don't sum to exactly 100?
The tool requires targets summing to 100% to calculate correct allocation percentages. If your sum is off, check for rounding: targets of 33/33/34 are fine; targets of 33/33/33 leave 1% unallocated. Adjust any single target by the rounding remainder to reach exactly 100%.
Should I include cash or money market holdings?
Yes, if cash is a deliberate allocation in your strategy — for example, a 5% cash buffer as part of your target. If cash is simply idle settlement funds waiting to be invested, excluding it from the allocation model and investing it first is usually the cleaner approach.
Can this model a portfolio with more than four asset classes?
The default view shows four holdings but the tool supports editing each row — you can rename and add specificity to any holding category. If your portfolio has six or eight distinct categories, enter them all with current values and targets. The drift and trade calculation works the same regardless of the number of rows.