Cost-Plus Rate Calculator

01 The problem

Quoting a cost-plus rate in a meeting meant opening a spreadsheet, finding the right tab, and trusting the formula was still current. That was slower than the conversation. It pulled my attention off the person in front of me and onto a file. One stale cell or a fat-fingered margin and I quoted the wrong number out loud. I needed the rate in my hand, not three taps and a leap of faith away.

02 The system

A single-screen calculator that does the markup math as you type. You enter the base cost and the terms, and the marked-up rate updates live. It installs to a phone like an app and runs fully offline, so a rate is ready on the spot, with or without signal. No tabs to hunt through, no formula to second-guess.

03 How it holds up

It is one self-contained file with no runtime dependencies. The pricing math lives in one reviewed function, following the integer-cents pattern used for money in code. Once installed, the calculator works without a network connection. Rate assumptions still need review when salary, benefits, overhead, or target margin changes.

04 The result

I can quote a rate in seconds with or without signal and stay in the conversation instead of opening a spreadsheet. The single-file build keeps maintenance small, while the commercial inputs remain easy to review and update.

05 Frequently asked questions

What is a cost-plus rate calculator?

A single-screen tool that does the markup math as you type. I enter the base cost and the terms, and the marked-up rate updates live. It replaces the spreadsheet I used to open mid-meeting, with no tabs to hunt through and no formula to second-guess.

Can a quoting tool work offline?

Yes. This one installs to a phone like an app and runs fully offline, so a rate is ready in a meeting with no connection needed. It works the same on a plane or in a basement as it does on wifi, which is the point of a tool you reach for mid-conversation.

Why build a calculator instead of using a spreadsheet?

The spreadsheet was slower than the conversation. It meant finding the right tab and trusting the formula was still current, and one stale cell meant quoting the wrong number out loud. The calculator keeps the math in my hand, so I stay with the person in front of me.

What does it take to maintain a single-file web app?

The build is small because it is a single self-contained file with no runtime dependencies. It still needs normal review when pricing policy or browser requirements change. The key advantage is that the math and inputs live in one visible place.