A portfolio worksheet can produce precise-looking totals from incomplete inputs. The decimal places do not make the missing facts disappear. Before comparing values or modelling a change, separate asset quantities, recorded costs, valuation assumptions and reporting currencies. Use fictional data for the exercise, and treat the result as arithmetic rather than a recommendation about what to buy, sell or hold.
Give each number a role
Create separate fields for quantity, unit price, price currency, valuation date and recorded cost. Quantity multiplied by the chosen unit price gives a value under those assumptions. Recorded cost is a different input with its own source. A current valuation does not tell you what was paid, and a transaction reference alone may not supply every fact required for that history.
Suppose a fictional holding contains three units valued at 40 USD each. Its scenario value is 120 USD. If the cost field is blank, you have not established a gain or loss. If the cost is explicitly recorded as zero with appropriate supporting context, that is a different state. The worksheet must not quietly convert the blank into zero.
Keep currencies consistent
Imagine another row has a value of 90 EUR. Adding it to 120 USD and labelling the result 210 USD would be incorrect. Either keep separate currency groups or use a documented conversion assumption, including the rate and date. Do not hide the conversion in a formula whose inputs disappear from the exported result.
The same care applies to fees. Record the fee asset or currency separately and explain whether a cost figure already includes it. An amount that has already been included should not be added a second time simply because there is another box labelled fees. If the treatment is unknown, keep that uncertainty visible for the appropriate reviewer.
Use scenarios as scenarios
A manually selected change of minus 20 percent explores a hypothetical outcome; it does not forecast a market move. Label the changed input and preserve the starting value. Compare scenarios by showing the same assumptions for each, rather than adjusting several hidden variables until one result looks more attractive.
For the fictional 120 USD holding, a 20 percent reduction in the assumed unit price produces 96 USD. That calculation says nothing about the likelihood, timing or suitability of an investment decision. A scenario table is useful when it shows sensitivity to inputs, not when it dresses an arbitrary percentage as a prediction.
Show incomplete totals honestly
Create a separate list of rows with missing costs, unknown currencies or unverified quantities. A subtotal of complete rows should be labelled as such. Do not present it as a complete account value or performance measure when excluded rows could materially change the result. Preserve the source of each manual correction instead of overwriting the only record.
Before exporting, ask whether someone could reproduce the result using the quantities, rates and dates in the file. Include unresolved items and distinguish original records from your calculated fields. This worksheet does not calculate tax or provide investment advice. Its purpose is to make the arithmetic inspectable, so an attractive chart cannot conceal a missing cost, a currency mismatch or a fictional assumption that has accidentally been presented as an observed fact.
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