How to use the portfolio allocation calculator
The page has three tools for turning money into positions.
Equal weight splits an amount evenly. Enter the amount and either the number of assets (for the dollar figure only) or a list of assets with their prices. With prices, the calculator rounds each position down to whole shares and shows the cash left over. The example splits $25,000 across five fictional assets.
Target weights splits an amount by the percentages you choose:
- Enter the amount to invest.
- Choose the unit size. Whole units suit most stocks and funds. Pick 2, 4 or 8 decimals for fractional shares or crypto.
- List the assets with their target weights and current prices. The weights can add up to less than 100%; the rest is held as cash.
Risk-capped crypto sleeve starts from the whole portfolio. Set the share you want in crypto, split that sleeve between coins, and test what a fall in crypto prices would do to the total.
The formulas
Unitsi = round down (Amounti ÷ Pricei, d decimals)
Leftover = Total − Σ Unitsi × Priceid is 0 for whole units. Actual weighti = Unitsi × Pricei divided by the amount invested (equal weight) or by the total (target weights).
Portfolio loss = Crypto allocation × Crypto decline
Crypto share after a doubling = 2a ÷ (1 + a)a is the crypto allocation as a decimal. The loss and the doubling assume the rest of the portfolio is unchanged.
A worked example
Equal weight. $25,000 across five assets is $5,000.00 each. At its price of $415.80, Stock C buys 12 shares; Stock D, at $28.90, buys 173. In total $24,742.45 is invested and $257.55 is left over. The largest gap between an actual weight and the equal 20% is 0.31%.
Target weights. $50,000 split 40/25/25/10 across four funds buys 168, 194, 129 and 20 whole units. That invests $49,682.35 and leaves $317.65 from rounding, with every weight within 0.36% of target.
Crypto sleeve. In a $200,000 portfolio, a 5% allocation is a $10,000.00 sleeve: $6,000.00 in Coin A, $3,000.00 in Coin B and $1,000.00 in Coin C. If crypto fell 50%, the sleeve would lose $5,000.00, or 2.50% of the portfolio.
Whole units, fractional units and leftover cash
Rounding down is what makes a real order list differ from the percentages on paper. In the target-weights example:
| Units can be bought in | Amount invested | Left over |
|---|---|---|
| Whole units | $49,682.35 | $317.65 |
| 2 decimals | $49,996.39 | $3.61 |
| 8 decimals | $50,000.00 | under $0.01 |
With whole units, the leftover per asset can be anything up to one unit’s price, so expensive assets and small amounts produce the biggest gaps. If an asset costs more than its share of the money, no unit can be bought at all and the calculator warns you. Fractional units remove almost all of the gap. Two practical points: check the decimals and minimum order size your platform supports, and remember that a leftover of a few hundred dollars is often best added to the next contribution rather than forced into an odd extra share.
Equal weight versus target weights
Equal weighting is a deliberate choice, not a neutral default. It gives the smallest asset the same influence as the largest, which spreads company-specific risk evenly and avoids letting one position dominate. Market-cap index funds do the opposite and weight by size. An equal-weight portfolio also needs regular rebalancing, because the winners grow past their share; our rebalancing calculator works out the trades.
Target weights suit portfolios built from different asset classes, where a bond fund and a stock fund should not have the same share simply because there are two of them. If you plan to hold the positions for a long time, the diversification calculator shows how concentrated the result is.
Sizing a crypto sleeve
Large crypto assets have historically been several times as volatile as a broad stock index, and they have fallen by more than 70% from peak to trough more than once. Sizing the sleeve as a fixed share of the portfolio puts a ceiling on how much such a fall can hurt:
| Crypto allocation | Sleeve on $200,000 | Portfolio loss if crypto falls 50% | Crypto share after a doubling |
|---|---|---|---|
| 2% | $4,000.00 | 1.00% | 3.9% |
| 5% | $10,000.00 | 2.50% | 9.5% |
| 10% | $20,000.00 | 5.00% | 18.2% |
The last column is the catch. A cap only holds if you rebalance: a sleeve that doubles while everything else stands still nearly doubles its share of the portfolio, and a much larger move can make it the biggest risk you own. Setting a ceiling in advance, such as the optional rebalance level in the tool, turns that into a rule. With a 5% target and a 7.5% ceiling, a crypto rise of 54% triggers a sale back to target.
The weights between coins work the same way as any other allocation. Holding several coins does not diversify much if they tend to move together, which crypto assets often do.
What this calculator does not include
- Trading costs and minimums. Commissions, spreads, exchange fees and minimum order sizes reduce what each position buys.
- Live prices. Prices move between the moment you calculate and the moment you trade; recheck before placing orders.
- Taxes. Buying does not create tax, but later rebalancing sales can.
- Suitability. The calculator does the arithmetic of an allocation. It says nothing about whether a given asset or weight suits your situation.