SONIA interest calculator
Work out the interest on a sterling loan priced as SONIA plus a margin: the all-in rate, the cost for any number of days, and how it changes if SONIA moves up or down. Free, no sign-up, nothing leaves your browser.
The starting rates are only an example; check today's SONIA on the Bank of England's website and your margin in your loan agreement. This uses simple interest on a 365-day year with SONIA fixed for the whole time. Real loans often compound SONIA daily or set it in advance, so your lender's figure may differ slightly. This is a calculator, not advice.
What SONIA is
SONIA, the Sterling Overnight Index Average, is the main benchmark interest rate for sterling. It measures the average rate banks and other large financial firms pay to borrow sterling overnight without security. The Bank of England publishes it every business day, and it usually sits just below Bank Rate and moves closely with it.
SONIA plus a margin
Many business loans and some mortgages are priced as SONIA plus a margin: the lender adds a fixed percentage on top of the benchmark. When SONIA moves, the rate on the loan moves with it, while the margin stays the same.
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