Stock Portfolio Value Calculator

Four position values, summed. On the sample figures 30,000 plus 25,000 plus 18,000 plus 12,000 gives a portfolio of 85,000, with the largest holding at 35.29% of it. The tool reports the total, the largest position and its share, how many slots are in use, and the average position size.

The concentration figure is the part worth looking at rather than the sum. A share is only a description of shape: it says how much of the total sits in one holding, and nothing about what that holding is or how it moves against the others.

A worked example

Suppose four positions worth 30,000, 25,000, 18,000 and 12,000 in the selected currency. The tool returns a total of 85,000, with the 30,000 holding at 35.29% of it. Adding 10,000 to that position takes the total to 95,000 and its share to 42.11%. Doubling it instead, to 60,000, takes the share to 52.17%. The figures update as each one is changed.

What moves the number most

Each position's lever is its own weight in the portfolio. Raising any one by 1% of its own value raises the total by that position's share of the total: 0.35% for the 30,000 holding, 0.29% for the 25,000, 0.21% for the 18,000 and 0.14% for the 12,000. Those four add to exactly 1%, which is what raising every position by 1% would do.

The largest-share row behaves differently, since it has the position in the numerator and the total in the denominator. Raising the largest holding lifts it, while raising any other holding lowers it, and the effect is strongest when the positions are furthest apart in size.

The formula behind this

The calculator performs a simple sum of all four position values. It then identifies the single largest position and divides it by the total to express concentration as a percentage.

Common scenarios where this matters

• Before adding a new stock purchase, to see how it will reshape overall concentration
• When assessing whether a single holding has grown too large relative to your plan
• For annual portfolio reviews, to track how positions have drifted from their original allocation
• When deciding whether to trim winners or add to smaller positions

What this captures and what it doesn't

The calculator shows your current total market value and concentration risk—the degree to which your portfolio is dependent on a single holding. It does not account for the sector or industry overlap between holdings, correlation during market stress, dividend income, fees, taxes on gains, or unrealised losses. Current values are a snapshot; they do not predict future performance or volatility. The concentration percentage is useful for identifying lopsided positions, but concentration alone does not measure diversification quality or risk.

For learning purposes

This calculator is designed for educational illustration. It models a simplified portfolio composition based on inputs you supply. Results do not constitute investment advice or a forecast of future outcomes.