Can AI build a tax estimator app like Keeper Tax?

Build a personal self-employment quarterly tax estimate calculator web app for my own use. This calculates an estimate only. It does not scan transactions for deductions and it does not file anything with the IRS.

Tech rules:
- Plain HTML, CSS, and vanilla JavaScript in one file. No framework, build step, account, or server.
- Store all data in localStorage under one key, with a version number.

Data model:
- IncomeEntry: id, type (1099 or W2), amountCents, quarter, year, withholdingCents (for W2 only).
- ExpenseEntry: id, description, amountCents, quarter, year.
- TaxProfile: filingStatus, state, priorYearTaxCents, stateTaxRatePercent (manually entered).

Features:
- Enter 1099 income and business expenses by quarter, and separately enter W2 income with employer withholding already deducted.
- Calculate net self-employment income (1099 income minus expenses) and apply the 15.3% self-employment tax rate to that figure, shown as its own line item, separate from federal income tax.
- Apply a rough federal bracket estimate to total taxable income (self-employment income plus W2 income minus a standard deduction), clearly labeled as an estimate, not a precise calculation.
- Show the 4 quarterly estimated payment deadlines for the tax year (mid-April, mid-June, mid-September, and mid-January of the next year), adjusted to the next business day if a date falls on a weekend or federal holiday.
- Recalculate the running estimate each time you add income or expenses for a quarter, rather than dividing one annual estimate by 4.
- A safe-harbor check: compare your year-to-date estimated payments against 100% (or 110% if your prior-year income was over $150,000) of your prior year's total tax, entered manually, and flag whether you're covered against an underpayment penalty even if this year's estimate turns out low.
- A state tax field where you manually enter your state's estimated rate, since state rules vary and some states have no income tax at all.

Edge cases the build must handle correctly:
1. Self-employment tax (15.3%) is calculated on net self-employment income only, never applied to W2 wages, which already have payroll tax withheld by the employer.
2. If a user has both 1099 and W2 income, W2 withholding already covers part of the year's tax liability, so the estimate must subtract it before calculating what's still owed.
3. Quarterly deadlines shift to the next business day when they land on a weekend or federal holiday; hardcode the standard 4 dates per year but flag adjustments as of the current tax year.
4. The estimate recalculates from year-to-date totals each quarter, not from one static annual number divided evenly, since income for the self-employed is often uneven.
5. Deductible business expenses reduce net self-employment income before the SE tax and bracket calculations, not after.
6. Standard vs itemized deduction: default to the standard deduction for the estimate, and label this assumption clearly, since itemizing changes the number and the app has no way to know which applies to the user.
7. The safe-harbor check uses whichever of 100% or 110% of prior-year tax applies based on prior-year income, and clearly states which threshold it's using.
8. Every number on the page is labeled "Estimate only, not tax advice" so it's never mistaken for a filed or reviewed figure.

Backup:
- One-click "Export JSON" and "Export CSV" of all income and expense entries by quarter.
- "Import JSON" restores after confirmation.

Layout:
- Mobile-first, readable at 375px wide, with the current quarter's estimated payment shown prominently at the top.

Exclusions:
- No publishing, App Store submission, accounts, bank transaction scanning, automatic deduction finding, e-filing, or any submission to the IRS. This tool produces a number for you to use when making your own estimated payment; it does not file anything.

Write a short README explaining where data lives, how to export and restore it, and stating clearly that this is an estimate tool only, not a substitute for a tax professional or for actual filing software.

Keep it under 600 lines. This is a personal tool, not a product.

What is the short answer?

Yes, but only for a narrow piece of what Keeper does. AI can build a self-employment quarterly tax estimate calculator, the SE tax plus a rough bracket estimate, in 2–3 hours for a basic version. It cannot replace Keeper’s Monthly plan at $20 a month, which is really a bank-transaction deduction scanner plus professional-reviewed IRS e-filing.

The scope here matters. This verdict covers only a DIY quarterly tax estimate number, a formula: self-employment tax plus a rough bracket calculation. It explicitly does not cover Keeper’s automatic deduction scanning from your bank feed, and it does not cover actual filing. A wrong DIY estimate risks real IRS underpayment penalties, and real e-filing legally requires IRS-authorized software, not a personal script. Build the estimate calculator if you want a running number between now and when you pay an accountant or file yourself; don’t treat it as a replacement for the rest of what Keeper does.

Option	Best for	Upfront cost	Ongoing cost	Main limitation
Build a rough prototype	Freelancers who want a quick SE tax + bracket estimate for one quarter	$0 and 2–3 hours	$0	Estimate only; no deduction scanning, no filing
Build a daily-use personal version	Freelancers who want a recalculating quarterly estimate with safe-harbor tracking	$0 and 6–8 hours	$0	Still no automatic deduction finding or e-filing capability
Keep paying for Keeper	Freelancers who want deductions found automatically and their return filed	$0	$20/mo Monthly, or $199–$1,199/yr for filing tiers	You’re also paying for services a DIY calculator can’t provide

The ready-to-paste starter prompt at the end of this page builds the daily-use estimate calculator only.

What should the first version include?

The first version should do one thing well: produce a defensible quarterly estimate number.

• Self-employment tax (15.3%) calculated separately from federal bracket estimate
• Manual entry of 1099 and W2 income with W2 withholding subtracted
• The 4 quarterly deadlines, adjusted for weekends and holidays
• A safe-harbor check against your prior year’s total tax
• Deliberate exclusion: no bank transaction scanning, no automatic deduction finding, no e-filing. This tool produces a number, nothing more.

What can AI build reliably?

ChatGPT and Claude reliably build the arithmetic for a self-employment tax estimate. The formulas (15.3% SE tax, federal brackets, safe-harbor thresholds) are publicly documented.

Concrete things AI gets right:

• Separating self-employment tax from federal bracket tax so the two never get combined into one wrong number
• Recalculating a running estimate as you add income and expenses through the year
• Applying the correct safe-harbor threshold (100% or 110% of prior-year tax) based on prior-year income
• Adjusting the 4 quarterly deadlines when they land on a weekend or holiday

Where will AI need human help?

The row’s core edge cases are all about correctness, not features. Mixed 1099 and W2 income changes how much tax is already covered by employer withholding, and getting that subtraction wrong overstates or understates what you still owe. Test the calculation against a known example, like a full-time W2 job plus a small freelance side income, before trusting it for real quarters.

State income tax is the other gap. Rates and estimated-payment rules vary by state, including states with no income tax at all. The starter prompt asks for a manually entered state rate rather than trying to hardcode 50 states of tax law, so you’ll need to look up your own state’s current rate.

The decision only you can make: this calculator estimates. Keeper’s actual product is bank-transaction deduction scanning plus a tax professional reviewing and e-filing your return, neither of which this build attempts. If you need deductions found automatically or you need to actually file, that’s Keeper or an accountant, not a DIY script. A wrong estimate has real consequences: IRS underpayment penalties are calculated on the shortfall, so don’t treat a formula you haven’t verified as gospel.

Privacy matters here, since income and expense figures are sensitive. Keep the data local with no account, and avoid pasting real dollar figures into a shared AI chat if that concerns you; use placeholder numbers while building, then load your real data after.

Can I get my data out of Keeper?

Yes, and it’s straightforward. From the Deductions tab, select the tax year and use the three-dot menu to choose “Export Deductions”. It produces a multi-sheet spreadsheet: a Schedule C category summary and a full transaction-level expense sheet, emailed to you or directly to an accountant.

The trap: the export covers only business expenses and deductions eligible for Schedule C, not a full income statement or the underlying bank transaction feed, and it does not export a computed quarterly-payment estimate as a standalone figure. If you’re switching to a DIY estimate calculator, you’ll still need to pull your income totals from your own bank statements or 1099s separately.

Note the trial: multiple complaints describe the 14-day free trial auto-converting into a full charge when users believed they’d cancelled in time [VERIFY, since these are third-party complaint reports, not from Keeper’s own documentation]. If you’re testing Keeper’s export before switching away, mark your calendar for the cancellation deadline.

How long will it take and what will it cost?

Rough prototype: 2–3 hours and $0. SE tax plus a bracket estimate for one quarter.

Dependable daily-use version: 6–8 hours, including safe-harbor tracking, mixed income handling, and quarterly recalculation. Build it on a free AI plan.

Keeper’s Monthly plan costs $20 a month for deduction tracking without filing. Since this build only replaces the estimate number, not the deduction scanning, a direct cost comparison isn’t meaningful; you’re not swapping one for the other, you’re building a smaller tool alongside whatever handles your actual deductions and filing.

These are estimates from reviewing the feature set, not measurements from a completed build.

Which AI tool or approach should I use?

Claude or ChatGPT on a free plan can build this, but treat it as an Intermediate build because of the tax math, not the interface. Ask the AI to show its formula for SE tax and the bracket estimate, and verify at least one full calculation by hand or against Keeper’s own free public quarterly tax calculator before trusting your build’s numbers.

Cursor is useful if you want to unit-test the calculation functions against a few known income scenarios.

Lovable is unnecessary here. There’s no need for a hosted database for a personal estimate tool.

What will I need to maintain?

Light, but tax law changes yearly.

Recurring work:

• Update the federal bracket thresholds and standard deduction amount each tax year, since these change annually
• Re-check the SE tax rate and safe-harbor percentages haven’t changed
• Re-enter income and expenses each quarter, since there’s no bank connection

Should I build it, buy it, or reduce scope?

Build it if you want a running quarterly estimate number and are comfortable verifying the formula, and you already have a separate system (or an accountant) for finding deductions and filing.

Buy it if you want deductions found automatically from your bank feed, or you want a tax professional reviewing your numbers before you pay them, or you need to actually file. Keeper’s Standard plan at $199 a year covers filing; the Monthly plan at $20 a month is deduction tracking only.

Reduce scope if you only need the deadline dates and a rough number once a quarter. Keeper’s own free public calculator already does this with no account needed, so there’s nothing to build.

Recommendation: use Keeper’s free calculator or build the narrow DIY estimate tool if all you want is a running number. Keep paying for Keeper, or hire an accountant, for the deduction scanning and actual filing; a DIY app cannot legally file your return, and a wrong self-calculated estimate carries real underpayment risk. If you also invoice clients or track billable hours as a freelancer, see the Invoice Ninja build or Toggl Track build.

What if I wanted to ship this to other people?

Shipping a tax estimate tool to other people means liability for wrong numbers that affect someone else’s real tax bill, a need for accuracy across every state’s rules, and IRS e-file authorization if you ever add actual filing. That’s a fundamentally different, much higher-stakes project than a personal estimate calculator you verify yourself.

Starter build specification

• User: You, a freelancer or self-employed person, estimating quarterly taxes for your own use.
• Problem: Wanting a running quarterly tax estimate number without paying $20/month for deduction tracking you may not need, or $199+/year for filing you’re not ready to switch.
• Core workflow: Enter income and expenses as they happen, see the current quarter’s estimated payment and safe-harbor status.
• Required features: SE tax calculation, federal bracket estimate, quarterly deadlines, safe-harbor check, manual state rate.
• Deliberate exclusions: No bank transaction scanning, no automatic deduction finding, no e-filing or IRS submission of any kind.
• Data ownership: Stored in localStorage. Exported as JSON and CSV. Imported from JSON.
• Definition of done: Entering a quarter’s 1099 income and expenses produces an SE tax figure and a bracket estimate that match a hand calculation, and the safe-harbor check correctly flags whether you’re covered.

For scoping help, read can AI build an app for me.

Sources and verification

• Keeper pricing: Monthly $20/mo, Standard $199/yr, Premium $399/yr, Business $1,199/yr.
• Keeper Exporting your deductions: export process and spreadsheet contents.
• Keeper’s free trial terms: 14-day trial auto-converts to a paid plan.
• Keeper’s free public quarterly tax calculator: a no-account reference point for checking your own estimate.

This app was not built and tested for this page. The verdict is based on Keeper’s official pricing and help center documentation, plus third-party review sites for the trial complaint pattern. Keeper’s price was checked on September 24, 2026.

Reviewed on September 24, 2026.