The net worth spreadsheet: build a good one, then retire it

Nearly everyone who tracks their net worth starts with a spreadsheet, and the good ones are genuinely good. Here is how to build one properly: the columns, the habits that keep it honest, and the two mistakes that quietly wreck the numbers. Then an honest word about when to retire it.

Respect the spreadsheet

The DIY net worth spreadsheet is one of the most useful documents a household ever makes. Building it forces the question most people never quite ask: what do we actually own, and what do we owe? People who keep one for a year learn their savings rate, notice fee creep, and make calmer decisions in a downturn because they have watched the line wobble before.

So none of what follows is mockery. A spreadsheet built well can serve you for years. The point is to build it well, because most are built in an evening and then trusted for a decade.

The columns that matter

Keep two sheets: a register of what you own and owe, and a history of valuations. The register wants a row per item with a name, a category (cash, investments, pensions, property, vehicles, crypto, valuables, and the debts), the currency it is held in, the owner if you share the sheet, and any tax wrapper such as an ISA or a SIPP. Liabilities are rows too: the mortgage, the car finance, the credit cards. Net worth is assets minus liabilities, and a sheet that ignores the minus side is a comfort blanket, not a measurement.

For the history sheet, resist the classic mistake of overtyping last month's value with this month's. Add a new row for each valuation: the date, the item, the value, and where the number came from. Overtyping destroys your own past. You can never again ask what the position was last January, or whether the total has actually grown, or how bad the bad year really was. Append, never overwrite.

A cadence you will actually keep

Match the effort to the asset. Bank and investment balances change daily and are easy to fetch, so monthly is fine. Property moves slowly: quarterly is plenty, and even then only when local sold prices give you a reason (how to value your house covers this). Cars can be updated twice a year. The watch, the art and the wine can be annual. A cadence that asks for an hour a month survives; one that asks for an evening a week is abandoned by March.

Whatever the rhythm, stamp every value with its as-of date. A net worth is only meaningful as of a moment. A sheet where the ISA is dated Tuesday, the house is dated 2023 and the car is a guess from memory produces a total with a false air of precision.

The FX mistake

If any of your money lives in another currency, dollars in a US brokerage account, euros in an account abroad, the common shortcut is to convert once at whatever the rate was that day and let the pounds figure fossilise. Sterling moves against the dollar and the euro by amounts that dwarf a savings account's interest in some years; hold enough abroad and the currency drift can outweigh your monthly saving without the sheet ever showing why.

The fix costs one extra column. Record the native amount and its currency, convert at the rate on the valuation date, and note the rate you used. Each historical row then still makes sense later, and you can tell the difference between the asset growing and the pound falling, which are very different pieces of news.

The pension mistake

Pensions are the largest asset most households have after the house, and the one most spreadsheets leave out, usually because nobody knows what number to write down. The result is a net worth that undercounts by five or six figures, and a plan built around the smaller, easier assets instead of the biggest one.

Defined contribution pots have a plain current value on the annual statement or in the provider's app: use it. Defined benefit promises and the State Pension need a stated convention rather than a market price, and there are respectable ways to do that: tracking pensions properly walks through them. A reasonable, labelled number beats a blank row every time.

Where a spreadsheet quietly fails

Formulas break silently: one deleted row and a sum range shrinks without complaint, and the total is wrong for months. History gets overwritten out of habit. Nothing reminds you to revalue, so the house figure ages until it is fiction. And the whole thing lives in one person's head: if your partner cannot find it, open it and understand it, the sheet fails the household at exactly the moment it is needed most.

None of these are character flaws. They are the natural behaviour of a general-purpose tool doing a specialist job, maintained by a person with a life.

The honest pitch

This is the job WealthWelly is built to do: every asset and liability in one place, values stamped with dates and exchange rates, history that appends rather than overwrites, reminders when a valuation goes stale, and pensions treated as first- class rather than left out. The spreadsheet taught you the discipline; software should now do the clerical work. Spreadsheets get the boot, and your data leaves with you whenever you want it, because export should be a button, not a negotiation.

This guide is general information, not financial advice; if you are unsure what is right for your circumstances, speak to a regulated financial adviser.