Can AI build a debt payoff planner app like Debt Payoff Planner?

Build a personal debt payoff planner web app to replace Debt Payoff Planner Pro for my own use. I use one device.

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:
- Debt: id, name, balanceCents, annualRatePercent, minPaymentCents, dueDay, createdAt.
- Payment: id, debtId, amountCents, date, isExtra (boolean), note.
- Plan: strategy (snowball or avalanche), extraMonthlyCents, frequency (monthly or biweekly).

Features:
- Add, edit, and remove debts with balance, annual interest rate, and minimum payment.
- Toggle between snowball (smallest balance first) and avalanche (highest rate first) ordering, and show both orderings side by side so I can compare total interest paid.
- Enter a monthly extra payment amount. The app allocates it to the top debt in the current ordering after minimums are covered.
- Show a projected payoff date and total interest paid per debt and for the whole plan, using compounding interest calculated at the debt's own rate and the chosen payment frequency.
- Log a one-time "snowflake" extra payment against a specific debt and recalculate the payoff date immediately.
- Toggle biweekly vs monthly payment frequency and show how it changes the payoff date, using the actual number of extra payments a biweekly schedule produces in a year (26 half-payments, not 24).
- When a debt's balance drops, recalculate its minimum payment if I mark it as "minimum recalculates with balance" (true for revolving credit cards, false for fixed installment loans).

Edge cases the build must handle correctly:
1. Snowball orders by balance ascending; avalanche orders by interest rate descending. Ties in avalanche break by smaller balance first.
2. If a debt's interest rate changes mid-payoff, let me edit the rate on a specific date going forward, and recalculate accrued interest only from that date, not retroactively.
3. A snowflake payment reduces principal immediately and recalculates the payoff date without needing to touch minimum payment amounts.
4. When calculating with different minimum payments and due dates across debts, apply each debt's minimum on its own schedule, not a single blended date.
5. Biweekly math must use 26 payments per year, and show the payoff-date difference against monthly clearly, since this is the feature Debt Payoff Planner charges for.
6. Compounding interest accrues daily on revolving debts (credit cards) and monthly on installment loans (auto, student), and the build must let me pick which per debt.
7. If I record a debt consolidation or refinance, let me close the old debt and open a new one with a link back to the original, so payoff history isn't lost.
8. A credit card's minimum payment recalculates downward as its balance drops (typically 1-3% of balance); a fixed installment loan's minimum stays constant. Let me toggle this per debt.

Backup:
- One-click "Export JSON" and "Export CSV" (one row per debt with current balance, rate, and projected payoff date).
- "Import JSON" restores after confirmation.

Layout:
- Mobile-first, readable at 375px wide, with a clear payoff-date summary at the top.

Exclusions:
- No publishing, App Store submission, accounts, payments, bank connections, or social features.

Write a short README explaining where data lives, how to export and restore it, and how I should manually verify the interest calculation against a known example before trusting the projections.

Keep it under 700 lines. This is a personal tool, not a product.

What is the short answer?

Yes, but. AI can build a snowball or avalanche debt payoff planner that replaces Debt Payoff Planner’s Pro tier, advertised as “from $2/month” on the official site [VERIFY, since the App Store lists $6.99 for one month], in 2–3 hours for a basic version.

The “but” is accuracy, not price. The app’s own pricing page calls its free plan “everything most people need for their journey,” and Pro mainly adds multi-device sync and biweekly payment math you can compute yourself with one extra formula. The real risk is compounding interest math done subtly wrong across debts with different rates and accrual schedules. Build it if you’re willing to check the numbers by hand for at least one debt before trusting the projections.

Option	Best for	Upfront cost	Ongoing cost	Main limitation
Build a rough prototype	People who want a snowball/avalanche comparison for a handful of debts	$0 and 2–3 hours	$0	Interest math unverified; check by hand first
Build a daily-use personal version	People who want biweekly payment math and snowflake payment tracking	$0 and 6–8 hours	$0	No multi-device sync; single device only
Keep paying for Debt Payoff Planner Pro	People who want their plan synced across phone and desktop	$0	From $2/mo per the site, or $6.99/mo per the App Store [VERIFY]	Free plan already covers most core planning

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

What should the first version include?

The first version needs correct interest math more than it needs features. A payoff planner that’s fast but wrong is worse than a spreadsheet.

• Multiple debts with balance, rate, and minimum payment
• Snowball and avalanche ordering, both viewable for comparison
• Payoff date and total interest projection
• Snowflake (one-time extra) payment logging
• Biweekly vs monthly payment frequency comparison
• Deliberate exclusion: no bank connections, no automatic payment scheduling. For a broader monthly budget alongside your debts, see the YNAB-style budget build.

What can AI build reliably?

ChatGPT and Claude reliably write the snowball and avalanche ordering logic and a basic amortization loop. The pattern is well documented.

Concrete things AI gets right:

• Ordering multiple debts by balance (snowball) or rate (avalanche), with ties broken consistently
• A payoff date projection that updates when you add a snowflake payment
• Total interest paid per debt and for the whole plan
• Switching between biweekly and monthly payment frequency and showing the date difference

Where will AI need human help?

Compounding interest across debts with different rates, frequencies, and accrual schedules (daily vs monthly) is the part most likely to go subtly wrong. The starter prompt asks the AI to let you pick daily or monthly accrual per debt, but you should still hand-calculate one debt’s next month of interest and compare it to the app’s number before trusting the rest.

Biweekly payment math is the second trap. A biweekly schedule produces 26 half-payments a year, not 24, which is one extra full payment annually. That’s exactly the acceleration effect Debt Payoff Planner charges Pro users for, so if the AI’s math treats biweekly as simply “monthly divided by two,” the projected payoff date will be wrong.

The decision only you can make is whether you trust a DIY calculator with real payoff planning. No official export exists to validate against, so there’s no vendor reference dataset to check your build’s numbers. If getting this precisely right matters to you, keep the subscription and its (presumably tested) math.

Privacy matters more here than with most personal tools, since debt balances and rates are sensitive. Keep the data local with no account, and don’t paste real balances into a shared AI chat session if that concerns you; use placeholder numbers while building, then load real data after.

Can I get my data out of Debt Payoff Planner?

Not officially. Neither the 1.0 nor the 2.0 help center documents a CSV, PDF, or spreadsheet export checked both help pages. A third-party comparison site claims “limited” CSV export exists, but doesn’t specify the format or which plan it requires. [VERIFY] this live in the app before relying on it.

The practical path: manually re-enter your debts (balance, rate, minimum payment) into your own build. For most people this is 3–6 debts, so it’s a 10-minute task, not a data-loss problem.

How long will it take and what will it cost?

Rough prototype: 2–3 hours and $0. Debt list, ordering toggle, and a payoff date estimate.

Dependable daily-use version: 6–8 hours, including biweekly math, snowflake payments, and per-debt accrual settings. Build it on a free AI plan, and budget extra time to hand-verify the interest calculation.

Pro costs from $2 a month per the site, or closer to $2.33 a month on the annual App Store rate [VERIFY]. A $20 month of a paid AI plan equals roughly 8-9 months of the annual rate. Build only on a free plan, or because you specifically want biweekly math the free tier doesn’t include.

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 this is an Intermediate build because of the interest math, not the interface. Ask the AI to show its formula and walk through one example calculation before you accept the code.

Cursor is useful if you want to iterate on the amortization function separately from the UI and test it with known numbers.

Lovable is unnecessary here. There’s no need for a hosted database for a single-device tool.

What will I need to maintain?

Minimal, but the math needs periodic sanity checks.

Recurring work:

• Update balances and rates after each statement, since nothing syncs automatically
• Re-verify the interest calculation if you add a debt type you haven’t tested (like a variable-rate card)
• Export a JSON backup periodically

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

Build it if you’re on one device, comfortable double-checking compounding interest math, and want biweekly payment acceleration without paying for it.

Buy it if you want your plan synced across your phone and desktop, or you don’t want to be the one responsible for catching a math error in your own payoff projection. Debt Payoff Planner Pro starts from $2 a month for that peace of mind.

Reduce scope if you have 1–2 debts and a simple payoff order. A single spreadsheet with a manual amortization formula does the job without building an app.

Recommendation: build your own if you’re paying off multiple debts on one device and are willing to verify the math once. Keep the subscription if you need multi-device sync or don’t trust yourself to catch a compounding-interest bug in your own build. For tracking overall spending alongside your payoff plan, see the YNAB-style budget build or Tally-style build.

What if I wanted to ship this to other people?

Shipping a debt payoff calculator to other people means your interest math needs to be provably correct for edge cases you’ll never personally hit (variable rates, unusual accrual methods, multiple currencies), plus liability concerns since people make real financial decisions based on the output. That’s a much higher bar than a personal tool you can hand-verify once.

Starter build specification

• User: You, for your own use, paying off multiple debts on one device.
• Problem: Paying a subscription for a snowball/avalanche calculator when the free tier covers most of it and the paid math (biweekly acceleration) is one formula.
• Core workflow: Enter debts, pick an ordering strategy, log payments and snowflake extras, watch the payoff date move.
• Required features: Multiple debts, snowball/avalanche toggle, payoff projection, snowflake payments, biweekly vs monthly comparison.
• Deliberate exclusions: No bank connections, no automatic payments, no multi-device sync.
• Data ownership: Stored in localStorage. Exported as JSON and CSV. Imported from JSON.
• Definition of done: Entering 3 debts with different rates, switching from monthly to biweekly, shows a payoff date at least one full payment cycle earlier, and the number matches a hand calculation for one debt.

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

Sources and verification

• Debt Payoff Planner official site: free plan description and “from $2/month” Pro pricing claim.
• Debt Payoff Planner on the App Store: $6.99 for 1 month, $27.99 for 12 months in-app purchase tiers.
• Debt Payoff Planner 2.0 help center: free vs Pro feature breakdown, no export documentation found.

This app was not built and tested for this page. The verdict is based on the vendor’s official site, its App Store listing, and its help center documentation. Debt Payoff Planner’s price was checked on September 24, 2026.

Reviewed on September 24, 2026.