InvoiceKoi

InvoiceKoi is aimed at the gap between a paper invoice book and full field-service software with dispatch and scheduling. It covers estimates, invoices, receipts, expenses and payments, and leaves out the office tools. You save clients with their address, terms and tax, keep a price book of your own rates, and fill an invoice by tapping a client and a few line items. An estimate can be signed by the client on your phone, and when the job is finished it becomes the invoice line for line.

The app works offline, which matters if you spend the day in basements and lofts. Sending a PDF, collecting card payments through Stripe and backing up to the cloud need a connection, but writing and saving don't. A daily reminder lists overdue invoices, and nothing is sent to the client automatically. There are nine PDF templates, and you can add your logo and an accent color.

Drafting is free and needs no account. Issuing new numbered documents needs a subscription. On the US App Store the solo plans are $99.99 a year or $9.99 a week, and eligible new iOS subscribers get two weeks free on the annual plan or one week on the weekly one. The subscription adds unlimited documents, all templates, time tracking, recurring invoices, reports, AI tools and photo backup. If you stop paying, you can still view, export and resend what you've already issued and record payments against it. The weekly plan works out far more expensive over a year, so the annual plan is the one to look at if you invoice regularly.

If you only need the occasional invoice, the website has a free browser invoice generator for the US and UK that makes a PDF without an account, watermark or upload.

The privacy policy, updated October 5, 2026, says that on a phone that has never signed in, nothing you type leaves the device. Three things leave the phone, each only when you press a button: a receipt photo you ask the app to read, a voice recording you ask it to transcribe, and, if you create an account, a backup copy of your books and receipt photos. Sign-in uses Apple, Google or an email link, with no password. The app sends crash reports, product milestones and subscription events to PostHog, and some builds measure ad installs through Meta. You can delete your account and its data from inside the app.

InvoiceKoi is built and run by Fang, a software company registered in Singapore. It's on Google Play now, and the iPhone app, which needs iOS 16.4 or later, is waiting on App Store review.