Portfolio Rebalancer Calculator
Calculate optimal buy orders for new cash contributions with our free portfolio rebalancing calculator to hit your target allocation: no selling required.
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How It Works
Portfolio rebalancing realigns your holdings back toward target allocation percentages. Over time winners grow overweight while laggards shrink, drifting you away from the risk profile you chose. This calculator focuses on buy only rebalancing: you add fresh cash and the tool tells you how many shares of each asset to purchase so post contribution weights move closest to policy targets without selling. Enter each ticker with shares owned, current price or use fetch prices for live quotes, target percentage, and the cash contribution you are adding today. Example: sixty percent equity and forty percent bonds drifting to seventy thirty after an equity rally means bond purchases should absorb most new cash until weights normalize. Policy portfolios often raise bond targets after equity rallies without requiring a sell ticket when new contributions arrive from payroll.
The engine computes total current value, adds your cash contribution to get total new value, then calculates target dollar value per asset as target percent times total new value. Shortfall per asset equals target value minus current market value. Buy orders allocate largest shortfall first, capped by remaining cash and whole share floor logic. Review before and after allocation bars, the shopping list with estimated cost per line, and unallocated cash when whole share rounding leaves residue. Shopping list cost estimates help confirm cash on hand before market open. Fetch live prices before executing so shortfalls reflect today's market rather than stale manual entries. Fractional share brokers can deploy leftover cash more fully than whole share floor logic shows here. Repeat after large market moves because drift changes which sleeve is underweight.
Review unallocated cash when whole share rounding leaves residue. Shopping list cost estimates help confirm cash on hand before market open. Fetch live prices before executing so shortfalls reflect today's market rather than stale manual entries. Fractional share brokers can deploy leftover cash more fully than whole share floor logic shows here. Repeat after large market moves because drift changes which sleeve is underweight.
Use Portfolio Rebalancer whenever inputs change: after market moves, new contributions, or revised personal assumptions. Bookmark the page for quick reruns without installing software.
Step by step
- Open Portfolio Rebalancer and enter your current inputs.
- Review calculated outputs and summary tables.
- Adjust assumptions and compare scenarios side by side.
Worked example
Portfolio rebalancing realigns your holdings back toward target allocation percentages. Enter the sample inputs described in How it works to reproduce the scenario step by step.
Adjust one input at a time to see sensitivity. Portfolio Rebalancer updates instantly so you can stress test optimistic and conservative assumptions before acting.
When to use this calculator
Reach for Portfolio Rebalancer when calculate optimal buy orders for new cash contributions to hit your target allocation: no selling required.. It suits quick what if analysis before trades, allocation changes, or plan updates.
Pair with related tools when the decision spans taxes, liquidity, or multi year projections beyond what one formula captures.
Common mistakes
Copying outputs without checking input units or stale market prices is a frequent error with Portfolio Rebalancer. Confirm tickers, percentages, and dates before acting.
Running a single baseline scenario ignores tail risks. Stress test with conservative inputs and compare against related tools listed below when the decision is material.
The Formula
TotalCurrentValue = Σ (sharesᵢ × priceᵢ)
TotalNewValue = TotalCurrentValue + CashContribution
TargetValueᵢ = TotalNewValue × (targetPercentageᵢ / 100)
Shortfallᵢ = TargetValueᵢ − (sharesᵢ × priceᵢ)
SharesToBuyᵢ = min(⌊shortfallᵢ / priceᵢ⌋, ⌊remainingCash / priceᵢ⌋)
Orders allocate largest shortfall first capped by remaining cash. Fetch prices before large contributions so shortfalls reflect current market values. Does not include trading commissions or spread costs. Whole share rounding may leave cash idle until the next contribution cycle completes.
Limitations and assumptions
Orders allocate largest shortfall first capped by remaining cash. Fetch prices before large contributions so shortfalls reflect current market values. Does not include trading commissions or spread costs. Whole share rounding may leave cash idle until the next contribution cycle completes. Portfolio Rebalancer does not replace personalized advice. Fees, slippage, account specific rules, and behavioral constraints may change real world outcomes.
Key terms
- What is portfolio rebalancing
- Portfolio rebalancing is the process of realigning portfolio asset weightings back to target allocation.
- Why should I rebalance without selling
- Selling triggers taxable events in taxable accounts.
- Model assumption
- Each asset shortfall equals target value minus current value where target value equals total new value times target percentage divided by one hundred.
Compare alternatives
Run ETF Overlap Detector before rebuying duplicate index funds, Portfolio Beta to check risk after trades, Maximum Drawdown Calculator to set cash reserves, and Tax Harvest Planner when sells become necessary in taxable accounts on portfolios. Use those calculators when portfolio rebalancer alone does not capture the full decision.
Internal links on portfolios.tools help you chain calculators: run Portfolio Rebalancer first, then validate edge cases with a specialized tool from the related section below.
FAQ
What is portfolio rebalancing?
Portfolio rebalancing is the process of realigning portfolio asset weightings back to target allocation. This calculator helps you buy the right amount of each asset with new cash contributions with no selling required. It suits taxable accounts where selling winners triggers capital gains you want to defer. Monthly dollar cost averaging from payroll can be steered toward the largest shortfall names until weights drift back toward policy targets. Roth accounts may still prefer buy only rebalancing when you want to avoid realizing gains inside the account before retirement. Rebalancing restores the risk return profile you designed rather than the accidental profile markets created.
Why should I rebalance without selling?
Selling triggers taxable events in taxable accounts. Directing new contributions to underweight assets rebalances tax efficiently while staying invested. Monthly contributions from payroll can flow to the largest shortfall until weights normalize. This approach works best when you have regular inflows. Without inflows, drift may exceed bands until you accept sells or transfers. Pair buy only rebalancing with tax loss harvesting when sells become necessary. In tax advantaged accounts, selling to rebalance has no immediate tax cost though transaction costs still apply.
How is the buy order calculated?
Each asset shortfall equals target value minus current value where target value equals total new value times target percentage divided by one hundred. Shares to buy equals floor of shortfall divided by price. Orders allocate largest shortfall first and cap by remaining cash contribution. Fractional share brokers deploy leftover cash more fully than whole share floor logic here. Fetch live prices before large contributions so shortfalls reflect current market values. If multiple assets share similar shortfalls, order priority follows descending shortfall sort. Unallocated cash appears when no whole shares fit remaining budget.
What if my targets don't add up to 100%?
Target percentages must sum to one hundred percent. The calculator shows a warning when entered targets sum to anything else and results may not reflect intended portfolio. Policy targets often differ from current weights after a long bull run in one sleeve such as US growth. Tactical bands such as five percent drift around targets are a human rule this strict one hundred percent target form does not enforce automatically. Normalize targets before running the tool. If you intentionally hold cash as an asset class, include a cash line with its own target percent.
Does this tool support fractional shares?
Buy orders round down to whole shares. Leftover cash after filling largest shortfalls shows as unallocated cash. Deposit unallocated cash on the next contribution cycle or add manually to the still underweight asset. Some brokers offer fractional shares on ETFs which deploys nearly all cash in one session despite floor rounding here. Options and mutual funds with different tickers in 401k versus taxable accounts require separate rebalance runs per account. This tool does not model transaction commissions or bid ask spread costs. For six figure contributions, even small price drift between calculation and execution can shift final weights by a few tenths of a percent: refetch prices immediately before placing orders.
How do I use this portfolio rebalancing calculator on phone or tablet?
Yes. Portfolio Rebalancer runs entirely in your mobile browser with the same formulas as desktop. Optional localStorage may remember inputs on your device when enabled in browser settings.
Where is my data stored when I use Portfolio Rebalancer?
Nowhere on our servers. Calculations execute locally in your browser. Optional localStorage saves form fields on your device only and never transmits portfolio numbers over the network.
Should I rely on Portfolio Rebalancer for tax or legal decisions?
No. Portfolio Rebalancer provides educational math only. Tax law, account rules, and personal circumstances vary. Consult a qualified tax or legal professional before transactions with material consequences.
Related Tools
Run ETF Overlap Detector before rebuying duplicate index funds, Portfolio Beta to check risk after trades, Maximum Drawdown Calculator to set cash reserves, and Tax Harvest Planner when sells become necessary in taxable accounts on portfolios.tools. Repeat after large market moves because drift changes which sleeve is underweight. Dollar Cost Average Pricer helps track cost basis on positions you add through repeated contributions.