Does a bidet actually pay for itself?

A calculator that answers honestly — including the parts that turn out not to matter.

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1 · The boring, defensible arithmetic

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to pay back the hardware

2 · The part people actually feel

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never think about it again

Toilet paper is the canonical shortage good. During a shortage you either pay the markup or you go without — and “go without” has no price, because there is no substitute. A bidet converts a good you can be denied into one you cannot. The dollar figure above is only the part that can be priced.

The number that decides everything

Bidets reduce paper — they don’t eliminate it, because most people still use some to dry. Typical honest range is 60–90%. Any calculator that zeroes your paper is overstating the answer by about a third.

75%
0%
no change 50%
sceptic 75%
typical 95%
towel-dries

Household & paper

US average is roughly 1.5–2.

The bidet

Non-electric seat attachment ~$40–80. Electric seats $300–600.

Most attachments are DIY. Put a plumber call-out here if you need one.

Water & sewer

This one costs you money, so we compute it — including sewer, which is usually billed on water volume and is often the bigger half. It is the term with the most room to embarrass us, so the defaults are set on the expensive side.

Deliberately high. Most people use the bidet roughly once a day, after a bowel movement — the default of 3 roughly triples our own running cost, which is the direction an honest default should err. Drop it to 1 if you want the realistic figure.

Typical 0.10–0.15 gal (0.4–0.6 L).

The emergency run

Nobody drives to the store for toilet paper, so we don’t count your grocery trips. Only the marginal run you make because you ran out. Expect this term to come out near zero — that’s the point.

Risk terms probabilistic

These two are expected values, not bills. They are shown separately from the arithmetic above precisely because they are guesses about the future. Zero either one and watch the answer move.

Kid incident front-loaded

The bathroom-as-water-park risk: towels, time, mopping. It happens in year one, then they learn. An expected-value term implies it recurs forever — this one does not, so we charge it to year one only. Mitigation: a non-electric attachment with the pressure dial turned down, or a model with a child lock.

0.30 with children under 10. No kids? Set it to 0.

Panic buying the hedge

Storms and shortages. 2020 proved it; every hurricane season repeats it in miniature. This is the only term that is really insurance rather than a discount.

0.25 on a hurricane coast; lower inland.

Display

Converts the water and fuel inputs in place. The model is unit-agnostic.

Every term, shown

The intermediate numbers are the proof the model isn’t rigged. Two of them are deliberately unimpressive.

Toilet paper displaced —
Marginal emergency run avoided —
Water + sewer used —
Net, hard arithmetic only — no probabilities in this line
Panic-buying premium avoided expected —
Kid incident year one only —
Net saving, year one — includes both risk terms
Net saving, year two onward — kid incident has aged out
Capital, amortised —
Net over 10 years —

What actually moves the answer

Each input nudged ±20%, holding everything else fixed. Longest bar = the input worth arguing about. It is almost always the reduction slider or the price of a roll — which is another way of saying most of the other inputs on this page don’t matter much, and you should know that.

    Where this is deliberately conservative

    Paper is reduced, not eliminated

    The single most common way these calculators lie. Most people still dry with paper, so the honest range is 60–90%. It is a slider here, never a checkbox, and the default (75%) is on the cautious side of typical. If you dry with a towel, move it up. If you don’t believe any of this, move it to 50% — the answer is usually still positive, and that is the argument.

    The fuel term is mostly fake, so it is kept tiny

    Attributing a whole grocery trip’s fuel to toilet paper is the classic error. Only the emergency run — the one you make because you ran out — is counted, and even that is scaled by the same reduction slider. For most households it lands under a couple of dollars a year.

    The water cost is computed against our own interest

    A bidet uses roughly 0.10–0.15 gal (0.4–0.6 L) per use. Sewer is included, because it is usually billed on water volume and is frequently the larger charge. The result is a rounding error, and showing a rounding error is more convincing than omitting it.

    The risk terms are quarantined

    Both are expected values — probability times cost — and are displayed on their own rows so you can see exactly how much of the headline is a guess. The kid incident is charged to year one only, because children learn. The payback figure is computed by walking month by month, so a year-one cost delays payback the way it actually would rather than being smeared across a decade.

    What is not modelled

    Plumbing risk, the value of your own time, resale value, septic pump-out intervals (real money for rural households — a possible second page), water heating if you fit a warm-water unit, and the environmental case. All of those are arguable; none are here. Nor is the one that matters most: the hedge value has no defensible dollar figure, and we don’t invent one.