How to compare two rates
Two percents are comparable only when they describe the same kind of balance for the same length of time.
Put both offers in the same tool
A 0.3 percentage-point gap between a 6.5% mortgage and a 6.2% mortgage is not a 0.3% difference in living costs. Type each rate into the mortgage page with the same price, down payment, term, tax, and insurance. The monthly-payment difference is the difference in cash leaving each month. The total-interest difference is how much more interest you pay. A longer term can lower the monthly payment and still raise the interest.
Do the same for a personal loan on the loan page. If one offer is level payment and the other is equal principal, switch the repayment style rather than forcing them into one shape. Then compare total interest and the first payment, not a single monthly number that does not exist for the equal-principal loan.
Do not mix a savings rate with a loan rate
A 7% savings rate and a 7% loan rate are not offsets. Savings interest in these tools lands on a growing balance with deposits. Loan interest lands on a shrinking balance. The currency units will not match even when the percents do. Pay down a high-interest card before celebrating a small savings rate. The credit-card page shows the interest a slow payoff still costs.
A promotional 0% period is a different product from a 0% rate for the whole term. Split the timeline. Run the promotional months as a zero-rate loan or as simple subtraction of payments, then run the remaining balance at the later rate.
Nominal, effective, and the rate on a sign
Loans, mortgages, credit cards, compound interest, savings goals, and the nominal retirement balance use a nominal annual rate divided by 12. Inflation, and the purchasing-power line on the retirement page, use a yearly factor. ROI reports a compound annual rate from two amounts you already know. Percentage, discount, tax, pay, and bill splitting do not compound. If a bank advertises an effective annual rate, typing it into the nominal field double-counts the compounding. Convert it, or note that the result is a little high.
Inflation is a third rate. A 5% savings return at 3% inflation is not a 5% gain in purchasing power. The retirement page restates a balance in today's money. The inflation page restates one amount. Use them after you have the nominal result, not instead of the loan schedule.
A short checklist before you trust a comparison
Match the term, the fees, and the payment style. Write down which number is a sample and which number came from an offer. If the offer includes a fee the field does not have, add it to the amount borrowed or keep it beside the result in your own notes.
If the two results are close, a fee or a tax you skipped is large enough to flip the winner. Close results are a reason to read the contract, not a reason to average the rates.
Related tools
These figures are estimates you can recompute from the formula on the page. They are not a lender quote, a tax bill, a payroll statement, or financial advice.