We are the MonoTape team. Sales tax turns simple prices into a small daily puzzle. A listing shows the price before tax, a receipt shows it with tax, and you are forever doing the conversion in your head to compare them or to fill in a form. The math itself is easy — multiply or divide by one-plus-the-rate — but a plain calculator makes you re-key it every single time. In this article we show how to keep both directions on a tape and flip between them in seconds.
Why the with-tax / before-tax flip keeps tripping you
The two conversions are mirror images. Before-tax to with-tax is a multiply: price × (1 + rate). With-tax to before-tax is a divide: price ÷ (1 + rate). Neither is hard, but on a calculator the result is a bare number with no memory of which direction you went or what rate you used. Do a few in a row and you lose track of whether 53.50 was the pre-tax or the final figure.
A notes app holds the prices but will not run the formula; a calculator runs the formula but forgets the prices. What you want is something that does the conversion and keeps the rate and both prices on named lines, so the relationship is always in view and easy to reuse.
Put the tax rate on one line and convert either way
In MonoTape you set the tax rate as its own labeled line, then build both conversions on top of it. Here a before-tax price goes up to its with-tax amount, and a separate with-tax price comes back down to before-tax — all at one rate.
Both directions live on the same tape, sharing one rate. You can read off that a $50 item rings up at $54.38, and that a $32.61 receipt was $29.99 before tax. Because every line is named, you never lose track of which price is which, even after a string of them.
Change the rate in one place and everything updates
Tax rates differ by state and city, and they change. The real win of putting the rate on its own line is that every conversion references that one line. Switch from 8.75% to 6%, edit the rate once, and both the with-tax and the before-tax figures recalculate together. No hunting through a dozen separate calculations to update each by hand.
A fair note: MonoTape is a calculator memo, not a tax or accounting tool. It does not look up local rates or file anything. It just lets you run the conversion and keep it, with the rate and both prices visible so the result is always checkable.
Flipping between with-tax and before-tax is a reuse problem, not a math problem. Set the rate on one line, convert in either direction, and edit the rate once to update them all. The conversion stops being a chore you redo and becomes something you read.
MonoTape
A calculator notepad where you label your math and one edit recalculates everything. Tax conversions, estimates, split bills — whatever you calculate stays on the tape. Free to use.
Learn more about MonoTapeFrequently asked questions
Does MonoTape know my local sales tax rate?
No. It is a calculator memo, not a tax tool. It does not look up rates or file anything. You enter the rate yourself on one line and it handles both conversions on top of it.
Can I go both ways — with tax and before tax?
Yes. Multiply by (1 + rate) for the with-tax price, and divide by (1 + rate) for the before-tax price. Both can live on the same tape sharing one rate line.
What if the tax rate is different?
Edit the single rate line and every conversion that references it recalculates at once. There is no need to redo each calculation by hand.
Is it free, and is my data private?
Yes, it is free, and everything is saved locally on your device, never uploaded. It works on both iPhone and Android.