What net worth means and how to track it

Net worth is one subtraction:

$$\text{Net worth} = \text{Assets} - \text{Liabilities}$$

Assets are everything you own that could be turned into money: cash and deposits, investment and retirement accounts, the resale value of a home and a car, a stake in a business, money other people owe you. Liabilities are everything you owe: a mortgage, student loans, car finance, card balances, tax due, an overdraft.

It is the household version of the balance sheet a company files. There the same residual is called equity, and it behaves identically: it is whatever the other two columns leave behind, and it moves the moment either of them does. There is no third column to act on. Every change in net worth is a change in what is owned or in what is owed.

Two conventions decide whether the figure means anything at all.

One date. Net worth is a stock, not a flow. A stock is a photograph of what exists at an instant; a flow is what moves during a period, which is what income, spending and cash flow measure. Two households showing the same net worth can be travelling in opposite directions, and one photograph cannot show that. Only a series of them can.

Debts at today's payoff balance, not at the total of the payments left. The payments still to come on a mortgage add up to more than the balance, and at a high rate to a great deal more. Every bit of that excess is interest that has not been charged yet and never will be if the loan is settled early. Subtracting the payment schedule counts money you have not borrowed.

Net worth is also one of the few figures in personal finance that can legitimately be negative, which the last section takes up.

Income is a flow. Net worth is a stock. Earning a large amount puts nothing on the balance sheet by itself, because money that arrives and leaves inside the same month leaves no trace in either column.

Only two things move the number:

$$\Delta \text{Net worth} = (\text{Income} - \text{Spending}) + \Delta \text{Value}$$

The first bracket is what you kept. The second term is what happened to the balances you were already carrying: investments rose or fell, a home was revalued, a car depreciated, a loan balance shrank as it was paid down. The revaluation part of it arrives with no decision from you at all, which is why net worth can climb in a year with no income and fall in a record one.

Spending reduces net worth whichever way it is paid for. Money spent out of cash leaves the first bracket. Money spent on credit leaves the first bracket untouched this month and adds the same amount to the liability column instead, so the reduction arrives anyway, unless the purchase puts an asset of its own on the other side. What financing adds in every case is the interest, and interest is spending with nothing on the other side at all. Two people paid the same for thirty years, one keeping a fifth of it and the other keeping none, do not finish anywhere near each other, and the gap has nothing to do with the salary they were both quoted.

This is also why wealth is hard to read from outside. A high income buys visible things, and net worth is invisible: it lives in account balances and in a mortgage getting smaller. Visible spending is net worth leaving the building rather than evidence of it arriving. Income is the engine that builds net worth. It is not the reading on the dial.

One rule covers most of it: count what a willing buyer would pay today, not what you paid. The cost-based figure has a name in accounting, book value, and for household goods it is close to fiction.

Retirement accounts are where the country decides the answer. In the United States, a traditional 401(k) or IRA balance is tax-deferred, so income tax falls due on withdrawal and the balance overstates what is spendable, while a Roth balance was funded with money already taxed. Which wrappers exist and how each is treated is set locally, which tax-advantaged accounts covers.

Two things do not belong on the asset side at all: a future salary and an expected inheritance. A pension that pays an income for life is the genuinely contested one. Some schemes will quote a transfer value on request, and the official wealth statistics in several countries do capitalise pension rights, so this is a choice rather than a settled rule. The convention that keeps the figure readable is to track a defined benefit pension on its own line, because a capital value that will never be paid out as capital inflates a total nobody can spend.

Precision matters less than consistency. The output is the comparison between dates, so an estimate wrong by the same amount every quarter still gives the right trend.

The home is the argument people actually have. Leaving it out while still subtracting the mortgage is plainly wrong: that removes a debt with no asset behind it. Counting it in full is not quite right either, since a home you live in cannot be spent without buying or renting another one.

The workable answer is to count it and keep a second line beside it. Total net worth includes the property. Liquid net worth, or investable net worth, drops the home and its mortgage, and answers a different question: what is available for anything other than living in.

What you own of it is the difference:

$$\text{Home equity} = \text{Market value} - \text{Mortgage balance}$$

Buying creates equity without creating net worth, which is the part people miss. On completion day the property arrives as an asset, the mortgage arrives as a liability, and the deposit moves out of cash and into equity: equity equal to the deposit, and a net worth unchanged by the swap. What does change is that the buyer's transaction costs leave and do not come back. Which costs those are depends on the country: legal or conveyancing fees and lender charges almost everywhere, a survey or a valuation in most places, and any transfer tax or stamp duty, which in some places runs to several percent of the price. Agent commission normally comes out of the seller's proceeds rather than the buyer's cash, though the arrangement varies. Net worth is lower the day after a purchase than the day before, by roughly those costs.

After that, two things move equity: the price, which can go either way, and the principal each payment retires, which only goes one way. The second is the quiet engine, and it starts slowly, because interest is charged on the whole balance at the start, so the principal slice of a level payment is at its smallest in the first month and grows every month after it. How amortisation works shows that split shifting period by period, and the loan payment calculator puts a schedule beside it.

A car runs the same arithmetic backwards. It is an asset at resale value, it depreciates fastest in its first years, and the loan behind it falls on a schedule that ignores the depreciation. Early in a long car loan the balance can sit above the vehicle's value, which is negative equity: the car is a net liability until the lines cross.

One reading carries almost no information. The same total can be a large house with a large mortgage behind it or a small one owned outright, a thirty year old or a sixty year old, a country where retirement is funded through personal accounts or one where it is funded by the state. What a single figure cannot say is whether assets are outgrowing debts, and that is the one thing the number is good at.

So take it on a schedule, always the same way. Quarterly is the usual choice, and the reason is signal rather than discipline: monthly turns ordinary market movement into events, and daily makes the whole exercise unreadable. Any fixed interval does the job as long as it does not change.

Three things move the trend, and they are worth separating.

• What you added. Income kept rather than spent. This is the part under your control.
• What the market did. Returns on what was already held, in either direction. Across a long run of positive returns this part grows relative to what you added, which is the mechanism set out in how compound interest works. In any particular year it can just as easily be the reason the total fell.
• What you repaid. Every loan payment shrinks the liability column. This is the engine nobody notices: a quarter where the cash balance fell but the mortgage fell further was a good quarter.

Telling the first apart from the second is what makes the series worth keeping. A rising market flatters a saver who did nothing, and a falling one hides real contributions, so the line on its own can applaud the wrong behaviour for years. Prices belong in it too, since a total growing slower than the cost of living is shrinking in what it buys, which is what inflation and purchasing power and the real return calculator measure.

Comparison with other people is mostly noise, because almost nothing in the list above is held constant between two households.

A negative net worth early in a career is arithmetic rather than a verdict. Money borrowed to study or to buy a car lands at the start, while the earnings and savings it was meant to buy arrive across decades. Someone who has just finished an expensive degree is often below zero for years, and the arithmetic that puts them there says nothing about how the money is being run. The question is the slope, not the sign.

The sign earns attention in three cases: when the debt behind it carries a high rate and is still growing, when the line has been flat or falling for years rather than months, and when the payments crowd out saving altogether, which is the ratio the debt-to-income calculator puts a number on.

The kind of debt matters as much as the size of it. A United States federal student loan on a standard plan is an ordinary balance that stays until it is repaid, though the income-driven plans alongside it set the payment from income and can end in cancellation after a long period, and the rules governing them are rewritten from time to time. In the United Kingdom, repayment is income-contingent by default and the balance is written off after a set period, so for many borrowers it behaves less like a mortgage and more like a payroll deduction, and reading the full balance as an ordinary liability overstates what will ever be paid. Which of the two you are holding is set by the loan agreement, not by the size of the number on it.

Two things the number does not measure, either of which can sink a household that looks fine on the line above.

• Timing. A large total can be locked inside a home, a pension and a business while nothing is available on Friday. That is a cash problem rather than a wealth problem, and it is what an emergency fund is for. What liquidity means separates the two.
• Concentration. A total that is one property, one employer's shares or one business is a different object from the same total spread across many, and only the second survives a single thing going wrong, which is the case diversification makes.

This is educational material rather than financial advice.