The Home Buyer's Calculator Pack — Eight linked calculators, every formula checked by recalculation

Eight calculators for the questions a house actually poses, in the order you meet them. Overwrite the blue cells with your own numbers; everything else follows. If you have five minutes, start with sheet 2 -- the true monthly cost is the figure easiest to get wrong, and on the worked example it is 40% more than the mortgage payment. Every formula in this workbook was recalculated and checked against an independent implementation before it shipped; see the Verification sheet.

What is in it

8 calculators, one per sheet. Overwrite the blue cells with your own numbers and everything else follows — nothing is locked, there are no macros, and it opens in Excel, Numbers, LibreOffice and Google Sheets.

• Mortgage payment — What is the monthly payment, and what does the loan cost in total?
• True monthly cost — What does the house really cost a month, not just the mortgage?
• Round-trip cost — What does it cost to buy and then sell again?
• Rent versus buy — How many years before buying beats renting?
• Overpayment timing — What is a lump sum worth, and does it matter when you pay it?
• Regular overpayment — What does an extra amount each month take off the term?
• Discount points — Is paying for a lower rate worth it, and after how long?
• What you can afford — What price do the usual lending ratios actually support?

Every formula was checked

This pack contains 45 formulas. Before it was published, every one of them was recalculated by a spreadsheet engine and compared against an independent implementation of the same arithmetic written in Python. All 45 agreed to within a cent, and the workbook carries a Verification sheet saying so.

That is an unusual thing to be able to claim about a spreadsheet, and it is the main reason to buy this one rather than download a free template. A formula that looks right and is wrong is worse than no formula at all, because you will act on it.

What each calculator assumes

There is a sheet listing this, because a calculator that hides its assumptions is just a number generator:

• A fixed rate for the whole term, and no overpayments.
• A maintenance allowance of 1% a year, averaged. Real spending is lumpy -- a roof is several years of it at once.
• 3% buying and 7% selling are example figures; they vary by market. Put your own in -- the selling side is the one that is easy to forget.
• No tax deduction, and no credit for investing the deposit instead. Both move the answer; both depend on things a spreadsheet cannot know about you.
• The overpayment goes to PRINCIPAL. Ask your lender -- some apply it to the next instalment instead, which does almost nothing.
• The extra is paid every month from the start and goes to principal.
• You keep the loan past the break-even. If you might move or refinance sooner, points are a prepayment for a benefit you will not collect.
• The 28/36 ratios are conventional and lenders vary. They also use GROSS income, which is why an approval can feel comfortable on paper and tight in practice.

What this is not

Not financial, tax or legal advice, and not a recommendation to buy, sell, borrow or sign anything. These are calculators: they show what a choice costs, not which choice is right for you. Where a published rate or threshold is used it is the one current when the pack was built — those change, the arithmetic does not.

Honest about the format

One .xlsx workbook, 8 calculator sheets plus Start Here, Assumptions and Verification. Not a PDF, not a physical product, not a Notion template. Available immediately after purchase; nothing ships.

Refunds

If this isn't what you expected, email me within 30 days and I'll refund you in full — no need to explain. Because it's an instant download I can't take the file back, so I'd rather you just had your money back.