Two different notions
Value is what a portfolio is worth on a given date. Performance measures what the investments earned or cost, excluding the money you added or withdrew.
Key takeaway
Worked example
A portfolio is worth €10,000 on 1 January. During the year you pay in €1,500. On 31 December it is worth €12,000. Its value rose by €2,000, but €1,500 came from your contributions: the gain from the investments is €500.
There are several ways to compute a performance percentage depending on how the timing of contributions is taken into account; they can give different results for the same portfolio.
When a value is unknown
Some values are not known continuously: euro funds, SCPIs, manually entered assets, tokens without a reliable price. An unknown value is not a zero value. Likewise, without a known cost basis, a holding's performance cannot be calculated.
Attention
In PortefeuilleZen
PortefeuilleZen distinguishes calculable, partial (some data is missing) and unknown performance, and never fills gaps with an invented estimate. Internal transfers, contributions and withdrawals are neutralised. An opening position starts its history on the declared date: no earlier history is reconstructed.