If your salary, savings, investments, or debts use different currencies, you need one reporting currency to calculate net worth. The aim is not to predict exchange rates. It is to create snapshots that remain comparable over time.
Choose a reporting currency
Use the currency in which you make most long-term decisions: usually where you live, pay taxes, or expect to spend the money. This is a reporting choice, not a recommendation to convert every account.
Keep each item’s original currency and original balance in the source record. Add converted values as a separate layer. Otherwise, you lose the ability to explain whether a change came from saving, market performance, or exchange rates.
Use one rate set per snapshot
Pick a reputable reference source and record the rate date. The European Central Bank publishes euro reference rates on working days, normally around 16:00 CET. It also states that these rates are for information and are not intended as transaction prices.
For a monthly snapshot, use one consistent convention—for example, the last published reference rate on the final working day of the month. Do not use Monday’s rate for one account and Friday’s rate for another.
If the reference source quotes every currency against the euro but your reporting currency is pounds, calculate a cross-rate from the same rate set. Avoid mixing providers unless a currency is genuinely unavailable.
Convert assets and debts the same way
Suppose your reporting currency is EUR and the snapshot contains:
| Item | Original value | Snapshot rate | EUR value |
|---|---|---|---|
| UK savings | £12,000 | 1 GBP = €1.16 | €13,920 |
| US brokerage | $25,000 | 1 USD = €0.85 | €21,250 |
| EUR cash | €8,000 | 1.00 | €8,000 |
| GBP loan | −£4,000 | 1 GBP = €1.16 | −€4,640 |
Converted net worth is €38,530. Keep more precision in the calculation than you display so repeated rounding does not create small unexplained differences.
Separate money movement from currency movement
One total is not enough for a useful monthly review. Track three components:
- Contributions and withdrawals: money you added, spent, borrowed, or repaid.
- Investment or asset movement: changes in the original currency before conversion.
- Currency effect: the change caused only by applying a new exchange rate.
A foreign account can fall in your reporting currency even when its local balance rises. That is not a bookkeeping error. Conversely, a favourable exchange-rate move can make net worth rise without any saving or investment return.
A practical comparison is to calculate the current portfolio twice: once with the current rates and once with the previous snapshot’s rates. The difference between those two conversions is the approximate currency effect.
Match the rate to the purpose
Reference rates are appropriate for consistent reporting. They may be inappropriate for a purchase, tax return, transfer, inheritance, or legal valuation. Those cases can require the actual transaction rate, an official tax authority rate, or professional guidance.
Also distinguish liquid balances from assets whose value is only estimated. A foreign property valuation may be much less precise than the exchange rate used to convert it. Extra decimal places do not fix uncertain source data.
Make the system auditable
For every snapshot, store:
- the original amount and currency;
- the reporting currency;
- the rate, source, and rate date;
- whether the value is observed or estimated;
- the converted amount;
- a note for unusual movements.
Never overwrite the prior snapshot. Once the method is stable, changing the reporting currency or rate convention should be treated as a documented methodology change, not a quiet edit to history.
The system is working when you can explain a change in net worth without guessing whether it came from behaviour, markets, valuation, or currencies.
Sources
This article is general education, not personalized financial advice.