# How net worth history works

> Today's figure is computed live, earlier days come from daily snapshots, and anything with a market price is revalued as you look at it. That mix explains most of what looks surprising on the chart.

Your net worth chart is not one thing. It is built from three mechanisms, and knowing which applies
where explains almost everything that looks odd about it.

## Today is computed live

The rightmost point on the chart is not a stored value. It is calculated from your current balances
at the moment the page renders.

That is deliberate, and it guarantees one thing worth relying on: **the end of the chart always
equals the figure at the top of your dashboard**. They cannot drift apart, because they are the
same calculation.

## Yesterday and earlier come from daily snapshots

Once a day, Gylder records the balance of each of your accounts. Those rows are what the chart draws
for every day before today.

Snapshots are per account rather than one total. It costs more to store and is worth it: a single
total for the day cannot tell you later which account moved, and the per-account view is what makes
a change explicable rather than mysterious.

## Anything with a market price is revalued as you look at it

Here is the part that surprises people, and the reason the chart can change without you doing
anything.

For assets with a central price, which means your investments, crypto, and manual holdings that
track a market such as metals, Gylder does not simply replay the value stored in the snapshot.
It takes **the quantity you held on that date** and multiplies it by **the price on that date**,
at the moment you load the page.

So when a price series is updated or corrected, your historical chart updates with it. You did not
change anything; the underlying price data got better.

This is why you do not have to wait for a backfill to see a corrected past. Backfill still runs
behind the scenes to keep stored data consistent, but it is repair work rather than something
standing between you and an accurate chart.

## What each type does

**Bank accounts and brokerage cash** are stable. Their value on a day is what the snapshot recorded,
because a cash balance has no market price to revalue against.

**Investments and crypto** are revalued at read time from quantity multiplied by price.

**Manual holdings that track a market**, such as metals with a weight and a unit, behave like
investments.

**Manual holdings without a market price**, such as a property or a business stake, hold the value
you gave them, applied from the date of that valuation onward. See
[adding a manual asset](/guides/adding-a-manual-asset).

## Why a valuation date matters so much

Because history is built from dated values, the date on a valuation decides where its effect starts.

Valuing your house today at €450,000 does not make it worth €450,000 last year. It adds a point
from today, and the earlier part of the chart keeps whatever earlier valuations you have given it.
That is why entering your purchase price and past appraisals changes the shape of your history so
much. Without them there is nothing to draw before the day you added the property.

## Common surprises, explained

**"My chart changed and I did nothing."** A price series was updated, and the revaluation ran on
your next page load. Most often this is a security or crypto position, or a metal.

**"A holding appeared at today's value with no history."** It has one valuation, dated recently.
Add earlier valuations to give it a past.

**"An old position still shows a balance."** A provider that stops reporting a holding is not the
same as reporting zero. This is a known failure mode Gylder now guards against by retiring holdings
a provider no longer mentions, but only when it is certain the data was fetched completely, because
zeroing on a partial fetch would destroy real balances.

**"Today's total and the chart disagree."** They should not, by construction. If they do, that is a
bug worth reporting rather than a rounding artefact.

## What is not modelled

The chart is a record of value over time, not a performance measure. It does not separate money you
added from growth in what you already held. For that distinction, see
[time-weighted vs money-weighted return](/concepts/time-weighted-vs-money-weighted-return), which
is what the investments dashboard uses.