How many months can your money last? Water in, water out, one number

What this is

One of our published methods, written in plain language: what it can do, when to use it, what goes in and what comes out.

Why it matters

Most methods are published as papers or code. This one is written so you can decide whether it fits your problem before you invest time in it.

How to use it

Read the page top to bottom. If it matches your question, use the online tool - or subscribe and run it on your own data.

What you get

A clear answer on what the method does and does not do, plus a live curve from our own demand series. Free to read.

Free to readOnline tools from $5 per runSee it →

Demand curve read by this method — A live reading from our own demand series - the shape of the signal this method works on. 570 industries are tracked daily; this is one of them.

Data base: InfoGap own records - 391 Chinese cities x 8 dimensions, 213,208 city-industry rows, 40,499 POIs (central / lifechain, 2026-10-08).

InfoGap Algorithm Handbook · one algorithm per page · no jargon · formal name: Water pool theory

1In one line: what it does

Turn income and spending into "water in and water out", then see how many months the pool can last and whether the money left in it can grow on its own.

2When to use it

It helps in these three situations:

Your shop has income and spending every month, all the numbers are there, but you cannot say clearly whether you are actually safe.

What people usually do: look at how much is left on the card at the end of the month.

Use it: enter water in and water out, and it works out the net flow, the surplus ratio, how many months it can last, and gives a colour.

You want to know "if I get no business for half a year, can I hold out".

What people usually do: estimate it themselves on a calculator.

Use it: enter the pool size and the current water level and it gives "how many months it can last" straight away.

You have made money, but the money just sits in the account and does not move.

What people usually do: feel that "keeping it is the safest".

Use it: enter a "rate at which the money grows on its own" and see what the assets become after a year — most people find they wasted many years doing nothing.

3What goes in · what comes out

Inputs (this is the exact set used for the real run)

· One year's income (water in): 200000
· One year's spending (water out): 50000
· Most the pool can hold: 3000000
· How full it is now: 0.8
· The rate at which the money grows on its own: 0.15 (15% a year)
· How much there is at the start: 2000000

What comes out

These numbers came out of it on the spot, with not one character changed:

Net flow: 150000 (income minus spending)
Surplus ratio: 75%
Months it can last: 60
Asset change over one year: +153000
Water in quality: plentiful
Water out quality: healthy
Which cell it falls in: 🟡 Hidden trouble — strategy "check the outflow and plug the leak"
Risk: low-to-medium risk, trend: growing ↑

—— change income to 1000 and spending to 90000 ——
Net flow: -89000, lasts 0.1 months
Which cell it falls in: 🔴 Critical — strategy "emergency stop the bleeding + rebuild"

How to read it: Three numbers matter most: net flow, how many months it can last, and which cell it falls in. Here net flow is a positive 150,000 and it lasts 60 months, which looks very solid, yet the cell it gives is "hidden trouble" with the strategy "check the outflow and plug the leak". The meaning is: it is not that there is not enough money, it is that there is still something to plug where the money goes out. Note that even fully filled in it only reaches "hidden trouble" — there is no "completely fine" tier — so do not expect a green all-clear from it; it only tells you where you can still save.

📈One chart: water in, water out, how long the pool can hold out

A pool that looks perfectly healthy — why it is still graded “hidden trouble”.

4How to use it

There is no public calculator for this yet — the method above is the whole procedure, and on this site the inputs have to be keyed in by hand.

The inputs are six items: income, spending, pool size, current water level, the rate at which the money grows on its own, and starting capital. There is no web form yet, so these six numbers have to be filled in by hand.

Get one year's income and one year's spending ready
Then estimate a pool size and how full it is right now
Put the six items through the method above
Read the net flow, how many months it can last, and which cell it falls in

5Who it is for

Shop owners with steady income and steady spending; people who want to work out "how long can I hold out"; people who make money but have no idea how to get it moving.

6Common questions

Q: How is "how many months it can last" worked out?

A: It takes the water currently in the pool and divides it by the monthly net flow. So if the income figure is wrong, this number means nothing at all.

Q: My net flow is positive, so why does it still say "hidden trouble"?

A: Because its focus is "can this be better", not "is this dangerous". A positive net flow is the baseline; it would rather send you to look at the outflow column.

Q: How is it different from "that other water pool algorithm elsewhere"?

A: Two versions of the same core: one runs on a questionnaire, one runs on numbers. The numbers one gives more detail (how many months it can last, asset change). Using both together means working it out twice — pick one and stop.

7Related algorithms

pure-compound-six · can money breed money risk-grade · how dangerous is it right now four-dim-landing · can it actually be done ← Back to the Algorithm Handbook Handbook index

✓Why this scenario exists (where the content comes from)

This scenario comes from the records of the "algorithm meets demand" round: the Chongqing · gym need was run against several algorithms, and this one was judged "useful" because "with capacity / water level / rate the money grows → lasts 60 months, one-year assets +153000, water in “plentiful”, water out “healthy”".

The inputs and outputs above were obtained by re-running the numbers in the record: income 200,000, spending 50,000, pool 3,000,000, water level 0.8, growth rate 0.15 → net flow 150,000, lasts 60 months, "hidden trouble"; the control group income 1000, spending 90000 → "critical".

Source: row 44 of the on-site city × industry gap table (Chongqing · gym); the D4 record in the matched-need ledger.