Sage Systems Lab

Debt payoff strategy comparison,
built like a tool —
not an app.

Offline-first calculators for people who want to understand the system behind the numbers. No accounts. No subscriptions. No tracking.

View tools See assumptions & methodology →
01 — Fit

Who this is for

These tools are built for a specific kind of person. This section is intentionally direct so you can decide quickly if this is right for you.

✓  This is for you if
  • You have 2 or more debts and want to see a clear payoff plan
  • You want to compare Snowball, Avalanche, and Proportional strategies with your actual numbers
  • You want a one-time purchase, not a monthly subscription
  • You want your financial data to stay on your device — not uploaded to a server
  • You want exports, summaries, and print-ready output for real planning
  • You've tried free calculators and found them too limited or too vague
✕  This is not for you if
  • You need variable APR or balance transfer modeling
  • You want a budgeting app that syncs with your bank
  • You want ongoing coaching or advice
  • You only need a quick payoff date and don't care about strategy or assumptions
  • You're looking for investment or wealth-building tools

Sage Systems Lab builds decision-support tools — not motivational apps. The goal is structured clarity, not gamification.

02 — Tools

Current tools

Each tool is a one-time purchase. No account required. Works offline after download.

SS-FIN-003
Debt Payoff Suite
v2.0 — Available now

A multi-loan payoff planner that compares Snowball, Avalanche, and Proportional strategies side by side. Enter up to 6 debts, set your extra monthly payment, and see exactly which strategy saves more interest — with a full month-by-month breakdown.

Runs entirely in your browser. Your numbers never leave your device. No login, no tracking, no expiry.

Format Single HTML file
Debts Up to 6
Strategies Snowball, Avalanche, Proportional
Rollover Yes — freed minimums roll forward
Exports CSV, Print summary
Projection Up to 100 years / 1200 months
Privacy 100% offline
Internet Not required after download

One-time purchase · Instant download · No account required

View details → Get it on Etsy
SS-FIN-001 / SS-FIN-002
Additional tools
Coming soon

After-Tax Income Planner and Excel/Sheets Debt Tracker are in final preparation. Check back or follow the Etsy shop for updates.

03 — Comparison

How this compares to free calculators

Free online calculators solve one problem at a time. This tool is built for people managing multiple debts who need a complete picture.

Feature Free calculators Sage Systems Lab
Multiple debts at once Rarely Yes — up to 6
Strategy comparison (side by side) No Yes — Snowball, Avalanche, Proportional
Rollover behavior (freed minimums) No Yes
Full amortization schedule Rarely Yes — month by month
Data stays on your device No Yes — fully offline
No account or signup Often required Never required
CSV export No Yes
Print-ready summary No Yes
Subscription required Sometimes Never — one-time purchase
04 — Methodology

How the math works

Transparency about modeling assumptions matters for a financial tool. Here is exactly what the tool does and does not calculate.

Interest

Monthly compounding

APR is treated as a nominal annual rate divided by 12. This matches how most consumer lenders calculate monthly interest.

Payments

Constant budget model

Your total monthly payment stays fixed. When a debt is paid off, its freed minimum rolls forward to the next target debt.

Strategies

Three methods

Snowball targets lowest balance first. Avalanche targets highest APR first. Proportional distributes extra payment across all debts by balance weight.

Limits

What it does not model

Variable APR periods, balance transfers, fees, penalties, or new spending on revolving debt. Results are estimates for planning purposes only.

05 — FAQ

Common questions

Does this work without internet?
Yes. After you download the file, it runs entirely in your browser with no internet connection required. There are no external servers, no API calls, and no data sent anywhere.
What browsers does it support?
Chrome, Edge, Firefox, and Safari on modern desktop browsers. Mobile browsers may work, but the tool is designed and optimized for desktop use.
Is my financial data private?
Yes. All data you enter stays in your browser session. Nothing is transmitted to any server. There is no analytics, no tracking, and no account system.
What is the difference between Snowball, Avalanche, and Proportional?
Snowball pays off your smallest balance first — faster wins, more motivation. Avalanche pays off your highest APR first — mathematically optimal, saves the most interest. Proportional spreads your extra payment across all debts weighted by balance. The tool calculates all three with your actual numbers so you can choose based on your priorities, not general advice.
What does "rollover" mean?
When a debt is fully paid off, its minimum payment does not disappear — it rolls forward and gets added to your next target debt. This is how a proper debt snowball or avalanche actually works. Most free calculators ignore this and underestimate how fast you can pay off remaining debts.
Is this a subscription?
No. It is a one-time purchase. You download the file, it works forever, and there are no recurring charges.
Who built this?
Sage Systems Lab is a small independent product studio focused on building structured decision-support tools for financial clarity. Tools are designed to be precise, private, and durable — not feature-bloated or subscription-dependent.