INPUT AND EVIDENCE LEDGER
Declare the evidence and assumptions first.
| Field | Value | Origin |
|---|---|---|
| Purchase price | ₩800,000,000 | Illustrative scenario |
| Cash contribution | 40% / ₩320,000,000 | User assumption |
| Loan | ₩480,000,000 at 4.0% for 30 years | User assumption |
| Management fee | ₩270,000 per month | Illustrative complex estimate |
REPRODUCIBLE WORK
Rebuild the result one step at a time.
Loan principal
₩800,000,000 × 60%
₩480,000,000Monthly rate and periods
4.0% ÷ 12; 30 × 12
0.3333% and 360 paymentsEqual monthly payment
P × r(1+r)^n ÷ ((1+r)^n−1)
About ₩2,291,593Visible recurring outflow
Payment + management estimate
About ₩2,561,593 per monthDECISION READING
The narrow conclusion supported here.
The purchase price alone is not a household budget. Under these assumptions, the visible recurring outflow starts near ₩2.56M before acquisition tax, brokerage, insurance, property tax, repairs, moving costs, and opportunity cost.
SENSITIVITY
Change one input before trusting the result.
- Every ₩10M change in cash contribution changes the financed principal by the same amount.
- A different rate changes all 360 scheduled payments; see the separate rate-sensitivity case.
- Complex-level management data cannot reproduce one household's seasonal usage.
SOURCE SNAPSHOT
Open the source and check the role it supports.
BOUNDARIES
Stop where the evidence stops.
- This is not a lender quote or an eligibility decision.
- The example does not assert that an apartment is currently listed or available.
- Public transaction and management records may be delayed, revised, cancelled, or unmatched.
HUMAN ACCOUNTABILITY + AI USE RECORD
The owner is accountable; the technical checks were AI-assisted.
The TOOOLBOX site owner authorized the publication scope and remains the correction contact. AI assistance was used for drafting, implementation, arithmetic recomputation, and source-link checks. This record does not claim line-by-line human fact-checking or licensed professional review.
- Record ID
- TB-APT-01-20260907
- Owner role
- TOOOLBOX site owner and developer
- Technical check date
- 2026-09-07
- Human fact-check
- No separate human fact-check recorded
- AI use
- Drafting, code, arithmetic, and link checks
- Correction channel
- Public contact page
- Recomputed the ₩480M principal and 360-period payment from the declared price, cash share, rate, and term.
- Kept the ₩270K management amount labelled as an illustrative input rather than a K-APT observation.
- Checked that the conclusion stops before taxes, fees, repairs, eligibility, and property availability.
FROM EXAMPLE TO A LIVE TOOL OBSERVATION · SEPTEMBER 7, 2026
What APT actually returned for Gwacheon Tower
The ₩800M case above is a teaching scenario. To test its relationship to the working product, we also ran APT for Gwacheon with a ₩300M–₩1.5B price range, 59–100 m², five years of sale history, 50% LTV, 40% cash, 4% interest and a 30-year term. This is an automated browser observation of the product, not independent verification of the transaction register.
| Candidate displayed | 과천타워 · Gwacheon Tower · 80.9 m² displayed |
|---|---|
| Sale record displayed | ₩1.02B · contract date March 25, 2026 |
| Cash budget | 40% × maximum price ₩1.5B = ₩600M |
| Required loan | ₩1.02B − ₩600M = ₩420M; below the ₩510M LTV ceiling |
| Payment check | ₩2,005,144 monthly; APT displayed 201만원, rounded to ten-thousand-won units |
| Management-cost evidence | Unavailable in this run; the data request failed. No complete monthly total could be verified. |
The cash percentage applies to the search ceiling
The same “40% cash” label can be misunderstood. In the simple ₩800M example, 40% refers to that home's price. In the live search, APT converts the percentage of the maximum search price into a fixed cash budget and tests each candidate against that budget. Applying 40% again to the ₩1.02B candidate would produce the wrong loan. That distinction explains why a live search cannot be reproduced by copying only the interest rate.
A missing bill prevents a complete total
The independent payment agrees with the displayed financing amount. The management-cost request did not succeed, so adding the earlier illustrative ₩270,000 would falsely make this observed candidate look complete. The defensible result is a financing component plus an unknown management component. A current household bill or attributable complex record is still needed before comparing full monthly outflow.
Repeat the filters in APT, then check the original contract date, area and cancellation status in MOLIT's transaction system. Search results can change. This observation is not evidence of an available listing, lending approval or a verified current household bill.
Download the dated inputs and observed outputs (JSON). The file distinguishes official values, tool observations and controlled assumptions. It contains no personal borrower or employee data.
MORE APT DECISION NOTES
Test the result yourself.
This note preserves a dated calculation. Change the inputs in the live workspace, or compare another evidence pattern below. Live source availability and results can differ from the dated example.