How to calculate your net worth
Net worth is what you own minus what you owe. The formula fits on one line. The problem is that half of what you own is not in a bank account and the other half changes price every minute.
The side you own
Current and savings accounts, cash, crypto, stocks, ETFs, funds, pensions, gold, your flat, your car and what people owe you.
The most common mistake is forgetting illiquid assets. A flat is net worth even if you cannot spend it this afternoon.
The second most common mistake is counting the same money twice: if the deposit already left your account, it is not on both sides.
The side you owe
Mortgage, personal loans, purchase financing, outstanding card balances and, if you are self-employed, whatever you have accrued for the tax office.
That last line is the one most people forget. The VAT you charged is not yours: it is money you are holding for the quarter.
The detail almost nobody adds: the time
A net worth figure without a timestamp means nothing. If you hold crypto, this morning's number is already not the current one.
Any serious tool should tell you when each position was valued, and what it does when a price provider is down. Showing a zero because there is no price is worse than showing nothing.
How often to recompute it
Once a month is enough to make decisions. Daily only if it helps, and for many people it just adds anxiety.
What is worth doing is keeping a monthly snapshot: the curve says far more than today's number.
A worked example
Picture someone with 8,000 € in bank accounts, 15,000 € in index funds, 2,000 € in crypto, a flat appraised at 220,000 € and a car that would sell today for 9,000 €. Assets: 254,000 €.
They owe 140,000 € on the mortgage, 4,000 € on a car loan and 900 € on a credit card. Liabilities: 144,900 €.
Net worth: 109,100 €. Notice the flat is 87% of the assets. An optimistic valuation of the flat moves the number more than the whole fund portfolio does.
How to value what has no market price
The flat: take the average price per square metre in your area from a property portal and apply a 5% to 10% haircut for selling costs. The cadastral value is not a substitute; it usually sits far below market.
The car: what the same model, year and mileage is listed for, minus something for a quick sale. It drops every year and deserves a yearly update.
Pension plans: they count as an asset at their liquidation value even though you cannot withdraw them. If you want to be conservative, note the income tax you will pay on withdrawal too.
Money owed to you: only if you are reasonably sure of collecting it. A loan to a relative nobody mentions is not an asset.
Your net worth and the Spanish wealth tax are two different numbers
The Impuesto sobre el Patrimonio uses its own valuation rules (the highest of three values for property, the average balance of the last quarter for bank accounts) and a general allowance of 700,000 € plus 300,000 € for the main home, adjusted by each region.
The net worth you compute for yourself is a management snapshot: today's market prices, with a timestamp. The tax return is a fiscal snapshot at 31 December. They are not supposed to match.
Do it in two minutes
Fider's net worth calculator adds each block and gives you the result with no sign-up. If you want the number to update on its own with the price of your funds and crypto, the app does that and stores one snapshot a month.
Frequently asked questions
How do I find out my net worth?
Add the market value of everything you own (accounts, investments, property, vehicles) and subtract everything you owe (mortgage, loans, cards). The difference is your net worth. Write down the date you computed it.
Does my home count if it still has a mortgage?
Yes. The home goes in full on the asset side at market value, and the outstanding mortgage goes in full on the liability side. Never net one against the other before listing them.
How often should I recalculate it?
Once a month is enough to make decisions. Keep every monthly snapshot: the trend matters more than today's figure.
Is a negative net worth a problem?
It is common right after buying a home with a small deposit or finishing studies with a loan. What matters is that the curve rises month after month.