SKILL/TREE

See what an extra $200/month actually saves you.

Drop in your loan amount, rate, and term. Get a full amortization schedule plus side-by-side payoff scenarios — interest saved, years cut, exact payoff date — in one HTML dashboard.

$3.99
Works in Claude (Pro/Max/Team) or ChatGPT (Plus/Team) · paid AI plan required
Both Claude + ChatGPT packages included — you can't pick the wrong one.
Updated
Included
01Three-scenario comparison cards: Base vs +$100/mo vs +$500/mo (or your own amount + 2x).
02Full amortization table with crossover month bolded — the moment principal finally beats interest.
03Shows interest saved per scenario in dollars AND years cut off the payoff date.
04Outputs three formats every run: a print-ready HTML dashboard, a CSV, and a Google Sheets formula block with live formulas.
05Handles refinance break-even: 'Month 28 — if you stay longer, refi wins.' Lump-sum, biweekly, and mid-loan starting balances supported.
06Flags negative-amortization loans, PMI/escrow exclusions, and prepayment penalties instead of silently ignoring them.

What it does

A mortgage amortization calculator with extra-payment scenarios for homeowners deciding what to do with a few hundred dollars of slack. Drop in loan amount, rate, term, and (optionally) what you're already paying — get back a dashboard with three side-by-side scenarios: Base, +$100/mo, +$500/mo, or your own amount and 2x. Each card shows monthly payment, payoff date, time saved, total interest, and interest saved versus Base. Underneath that: a full month-by-month amortization schedule with the crossover row bolded (where principal finally beats interest), payoff rows highlighted under each scenario, and a stacked bar chart showing principal vs. total interest. Refinance comparisons get a break-even analysis. Lump sums, biweekly schedules, and mid-loan starting balances are all supported. Every run produces three outputs: a self-contained HTML dashboard (no external dependencies, prints clean), a CSV of the full schedule across all three scenarios, and a Google Sheets starter block with live `=PMT/IF` formulas you can drag down to row 369.

Frequently asked

How much does paying an extra $100 a month save on a 30-year mortgage?
On a $350k / 7% / 30-year loan, +$100/mo saves about $42,000 in interest and cuts roughly 3.5 years off the payoff date. The skill computes this exactly for your loan and shows it next to a +$500/mo scenario for comparison.
Should I refinance or just pay extra on my current mortgage?
Both. Tell it your current loan + the new rate + closing costs and it produces a break-even analysis (months to recoup closing costs from monthly payment savings) plus an extra-payment-on-current-loan scenario. If you plan to move before break-even, refi loses — the dashboard makes that obvious.
Does it handle biweekly payments and lump sums?
Yes. Biweekly is modeled as adding 1/12 of your monthly payment as an extra each month (the standard 26-half-payments effect). Lump sums are modeled as a one-time principal reduction in whatever month you specify.
Why is my actual mortgage payment higher than what this shows?
Because your bank statement payment includes escrow (property taxes + insurance) and possibly PMI. This dashboard covers principal + interest only — that's the part that amortizes. Escrow is a passthrough to your tax authority and insurer; PMI is a separate add-on. Both are flagged in the footer.
Can I just use Bankrate or NerdWallet instead?
Their basic calculators work for the headline number. This gives you a side-by-side three-scenario dashboard, a printable amortization table with the crossover row highlighted, a CSV, AND a Google Sheets paste block — so you can keep iterating without re-entering inputs every time.

Install — no Terminal required

After checkout you land on a page with a one-click download and a pre-built install prompt. Pick the AI you already pay for — both packages are included, so you can't pick wrong.

What you'll see the second your payment clears
Your license key
ST-XXXX-XXXX-XXXX · permanent
Pre-built install prompt⧉ Copy
ChatGPT package (ZIP)⬇ Download

No setup work before you buy — copy, paste, done.

Have Claude Pro, Max, or Team?
Copy the prompt, paste into Claude

Copy the pre-built install prompt from the success page, paste it into any Claude Code chat, and Claude installs the skill itself — about 10 seconds. Using the app instead? Drop the downloaded folder into a Claude Project's knowledge and ask Claude to use it.

Have ChatGPT Plus or Team?
Build a Custom GPT — ~2 minutes
  1. Click Download ChatGPT package (included with every purchase).
  2. Unzip it — inside is a SETUP.md and a knowledge/ folder.
  3. Go to chatgpt.com → your profile → My GPTs → Create a GPT → Configure.
  4. Paste the Name, Description, and Instructions from SETUP.md into the matching fields.
  5. Under Knowledge, upload every file in the knowledge/ folder.
  6. Click Create/Save, open your GPT, and describe your task in plain English.

A paid plan on either platform is required — Claude (Pro, Max, or Team) or ChatGPT (Plus or Team). Comfortable with Terminal? A one-line npx skilltree-network install path is available too.

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