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APT · CALCULATION WALKTHROUGH · NOTE 12

Use the official rate range as a stress band

A 30-year planning model tests 4.90% and 5.20% as an explicit range informed by HF's September endpoints, not as quoted 30-year products.

INPUT AND EVIDENCE LEDGER

Declare the evidence and assumptions first.

FieldValueOrigin
Planning principal₩300,000,000User scenario
Planning term30 yearsUser scenario; not an HF quote
Stress band4.90% to 5.20%HF September endpoint range
PurposeBudget resilienceEditorial calculation

REPRODUCIBLE WORK

Rebuild the result one step at a time.

01

Lower-band payment

₩300M, 4.90%, 360 payments

₩1,592,180 monthly
02

Upper-band payment

₩300M, 5.20%, 360 payments

₩1,647,333 monthly
03

Monthly buffer used

Upper − lower

₩55,153
04

Thirty-year scheduled difference

₩55,153 × 360

About ₩19.9M

DECISION READING

The narrow conclusion supported here.

A rate input should be a range, not a single reassuring number. In this controlled model, 0.30 percentage points consumes about ₩55K of monthly room before any management, tax, or repair cost changes.

SENSITIVITY

Change one input before trusting the result.

  • The absolute gap grows with the principal.
  • A shorter term changes both payment and cumulative interest.
  • The actual 30-year product rate must be checked directly; these are stress endpoints.

SOURCE SNAPSHOT

Open the source behind each factual layer.

HF September 2026 rate releaseSupplies the 4.90%–5.20% official endpoint range used only as a stress band.Official source · accessed 2026-09-02 ↗

BOUNDARIES

Stop where the evidence stops.

  • The range is an analytical band derived from published endpoint rates.
  • It is not a 30-year HF rate quotation.
  • Borrower-specific charges and eligibility are excluded.

OWNER AUTHORIZATION + VERIFICATION RECORD

One accountable operator and a reproducible check record.

The TOOOLBOX site owner authorized this publication scope and remains the correction contact. The checks below were completed during preparation with AI-assisted implementation; they are an audit record, not a claim of licensed professional review.

Review ID
TB-APT-12-20260902
Owner role
TOOOLBOX site owner and developer
Release scope
Owner-authorized · 2026-09-02
Correction channel
Public contact page
  1. Separated official source values from the user-selected 30-year term.
  2. Recomputed both 360-payment schedules and the difference.
  3. Added repeated wording that prevents the stress band from reading as a quote.

MORE APT DECISION NOTES

Compare another evidence pattern.

The related notes deliberately use different questions, data states, and editorial forms.

13 · A cancelled transaction must leave the price baseline →14 · Normalize area before comparing two sale records →