When to use this formula
Use this formula when your inputs match the variables and units shown below. It is most useful for checking a calculator result, recreating the calculation in a spreadsheet or understanding which input has the biggest effect.
Quick use
Use the formulas to compare scenarios, then check lender rules, tax treatment and local mortgage regulation before acting.
Formula
LTV = loan balance / property value; points cost = loan amount x points / 100; break-even months = upfront cost / monthly savings; balance-transfer savings = old interest cost - new interest cost - transfer fee.
Variables
Use the same currency and time period for loan balance, fees, monthly savings and interest assumptions. Property value should be clearly defined as purchase price, appraisal or current estimate.
Method notes
- Compare total cost as well as payment.
- Keep fees visible instead of burying them in the rate.
- Use clean scenarios when deciding whether a payoff, refinance or transfer is actually better.
Example
If refinance closing costs are 3,000 and the new payment saves 150 per month, simple break-even is 20 months before tax and prepayment assumptions.
Assumptions and limitations
Mortgage and debt rules vary by country, lender and product. These formulas do not decide eligibility, legal disclosure, tax deduction, credit risk or future rate changes.
When the formula is not enough
- If the result depends on live prices, rates or official thresholds, check the latest value from the named source before relying on it.
- If the topic is medical, tax, legal, lending or safety related, use the result as a learning aid and check primary guidance before acting.
- If units or time periods differ, convert them before comparing results.
- If rounding affects the decision, keep extra precision until the final step.
Common mistakes
- Choosing the smallest payment while extending the term dramatically.
- Ignoring transfer fees, points or closing costs.
- Using property value estimates that do not match lender definitions.
FAQ
Why look at the formula instead of only the answer?
The formula shows which inputs actually drive the result. That makes it easier to spot a wrong unit, compare two scenarios or explain the answer to someone else.
Can different calculators use different formulas for the same topic?
Yes. Some topics have multiple accepted methods or simplified variants. When that matters, the calculator should say which method it uses and what is excluded.
Are formula pages updated?
Stable math formulas need occasional review. Formulas that depend on changing rules, prices or thresholds need a dated source before the page can make stronger claims.