Does a bidet actually pay for itself?

Works out the paper, water, fuel and risk, and shows every figure that goes into the answer.

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1 · The arithmetic

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to pay back the hardware

2 · The shortage hedge

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never think about it again

Toilet paper is the first thing off the shelves in a storm or a scare. When that happens you pay whatever it costs, or you do without. A bidet takes you out of that market for good. The figure above prices the markup only — there is no sensible number for the years you simply cannot buy any.

How much paper you actually stop using

Most people still use some paper to dry, so a bidet cuts consumption by 60–90% for a typical household. A calculator that sets your paper use to zero overstates the saving by about a third.

75%
0%
no change 50%
skeptic 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

A bidet adds to your water bill. Sewer is included, since it is usually billed on water volume and is often the larger charge. The defaults below sit at the expensive end of the range.

Most households average about one bidet use per person per day. The default of 3 is set high, which raises the water cost shown below. Set it to 1 for a typical figure.

Typical 0.10–0.15 gal (0.4–0.6 L).

The emergency run

Grocery trips are excluded, because almost nobody drives to the store for toilet paper. This counts only the extra trip you make after running out. For most households it comes to a couple of dollars a year.

Risk terms probabilistic

Both terms below are a probability multiplied by a cost. Each describes an average year, and neither is a bill you will receive. Set either to zero to see the answer without it.

Kid incident front-loaded

Children discover the sprayer. Towels, time, mopping. Charged to year one only, since it stops once they have learned. A non-electric attachment with the pressure turned down, or a seat with a child lock, largely avoids it.

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

Panic buying the hedge

Storms and shortages. 2020 was the large version; hurricane season is the small one. This term behaves like insurance — it pays off in the years the shelves empty.

0.25 on a hurricane coast; lower inland.

Display

Converts the water and fuel inputs. The result is the same either way.

Every term, shown

Everything that goes into the total, including the two terms that come to almost nothing.

Toilet paper displaced —
Marginal emergency run avoided —
Water + sewer used —
Net, 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 no longer applies
Capital, amortized —
Net over 10 years —

What actually moves the answer

Each input moved ±20% with everything else held fixed. The longest bar is the input worth arguing about. Usually it is the reduction slider or the price of a roll; most of the rest barely move the total.

    How the numbers are worked out

    How much paper a bidet actually saves

    Most people still dry with paper, which puts the real range at 60–90%. The default of 75% sits at the cautious end. Move it up if you dry with a towel. At 50% the answer usually stays positive, so the slider is worth trying at whatever figure you believe.

    Why fuel barely registers

    Charging a whole grocery trip to toilet paper is the usual error here. Only the extra trip after running out is counted, scaled by the same reduction slider. For most households it lands under a couple of dollars a year.

    Why the water cost stays small

    A bidet uses roughly 0.10–0.15 gal (0.4–0.6 L) per use, and the rate above covers water and sewer together. The default of three uses per person per day is about triple what a typical household does. Even at that setting the water cost lands at a few dollars a year against a few hundred saved.

    How the two risk terms are handled

    Each sits on its own row, so you can see how much of the total is estimated. The kid incident is charged to year one only. Payback is worked out month by month, so a year-one cost pushes the payback date back by the right amount.

    What this leaves out

    Plumbing risk, the value of your time, resale value, septic pump-out intervals, water heating on a warm-water unit, and the environmental case. Septic is real money for rural households and deserves working out separately. The shortage hedge is absent from the dollar total too, because there is no defensible figure to put on it.