## Why standard mortgages struggle at auction
Auction contracts usually require quick completion. A standard mortgage may need valuation, underwriting, legal review, searches, title checks, and final offer conditions. If the legal pack reveals defects, short lease, missing consents, structural issues, or unusual tenure, the lender may slow down or decline.
HM Land Registry's [property information guidance](https://www.gov.uk/search-property-information-land-registry) helps investors understand title checks, but it is not a replacement for solicitor review. For tax cash, use the official [SDLT calculator](https://www.tax.service.gov.uk/calculate-stamp-duty-land-tax/) where SDLT applies.
## The finance calculation
Model three routes:
1. Cash purchase.
2. Bridging purchase with refinance or sale exit.
3. Standard mortgage only if the timeline and property condition are realistic.
Formula: total auction funding need = deposit plus balance on completion plus tax, legal fees, auction fees, lender fees, works, interest, contingency, and exit costs.
## Worked example
An investor wins a property at 180,000 with a 28-day completion deadline. The buyer assumed a standard mortgage, but the lender needs a valuation and the legal pack contains a title issue. A bridge at higher cost becomes the fallback.
If bridge fees and interest add 8,000 and urgent works add 12,000, the project now needs 20,000 more than the original spreadsheet. If the refinance valuation is also lower than expected, the bridge exit becomes the real risk.
## What to check before bidding
Check completion date, special conditions, title, lease, searches, planning, building control, access, utilities, occupancy, tenancy, and lender acceptability. Ask a broker whether the asset is mortgageable in its current state. Ask a solicitor whether the legal pack creates completion or resale risk.
## Better habit
Do not bid with a standard mortgage plan unless the lender, solicitor, and timeline support it. In most auction cases, the safer underwriting habit is to price the deal as if bridging is required, then treat a standard mortgage as upside if it genuinely completes in time.
## What to save in the model
For this why auction mortgages fail check, save the source links, date checked, calculator inputs, base case, downside case, professional question, and final pass or proceed decision in the deal notes. Also save who verified each assumption: broker, solicitor, council, insurer, accountant, or your own viewing notes. The article should not be the evidence itself. It is the checklist that tells you which evidence to collect, where to link it, and which calculator result changed the decision. For live deals, rerun the model whenever one assumption changes. If the answer changes, update the offer price before sharing the pack. Keep rejected assumptions visible too.