Commercial Mortgage Calculator | Shepherd Commercial

Commercial Mortgage Calculator

Commercial mortgages are one of the most common funding routes for buying, refinancing or improving business premises and investment property. They can also feel unnecessarily complex because lenders look at more than just the interest rate. The calculator above is designed to give you a fast, plain-English estimate of likely repayments under typical structures, so you can sanity-check a deal before you speak to a broker or lender.

What is a Commercial Mortgage?

A commercial mortgage is a loan secured against a property that is used for business purposes or held as an investment. That includes offices, industrial units, retail premises, roadside assets, mixed-use buildings and many forms of specialist property. Lenders are usually assessing two things:

• Security – the property’s value, condition, marketability and location.
• Affordability – whether the borrower can service the debt, based on trading performance, rental income, or both.

Unlike many residential products, commercial terms vary widely because every property and borrower profile is different. That’s why an early repayment estimate is useful: it helps you decide whether a deal is broadly workable before you spend time (and fees) moving forward.

Repayment vs interest-only: which is better?

Commercial mortgages are commonly structured on either:

• Capital + Interest (Repayment): you pay interest and gradually repay the loan balance over the term. The balance reduces each month (or quarter), and by the end of the term the loan should amortise down towards £0 (subject to rounding).
• Interest Only: you pay only the interest (and any voluntary overpayments) during the term. The original balance typically remains outstanding and is repaid at the end via refinance or sale.

Neither is “better” in isolation. Repayment reduces risk because the debt shrinks over time, but the monthly commitment is higher. Interest-only improves cashflow and can be suitable where the strategy is to sell, refinance, or where the property income comfortably covers interest and the borrower wants to preserve liquidity.

If you are buying as an investor, interest-only can make sense where you expect capital growth, want higher cashflow, or plan a defined exit. If you are an owner-occupier, repayment is often more conservative because it steadily builds equity.

The key factors lenders care about

When assessing a commercial mortgage, lenders typically focus on:

Loan-to-Value (LTV)

This is the loan amount as a percentage of the property value. In broad terms, lower LTV often means better pricing and easier underwriting. Higher LTV can be achievable but may involve tighter affordability tests, stronger covenant requirements, and higher interest rates.

Debt Service Coverage Ratio (DSCR)

For investment property, many lenders look at whether the rental income covers the mortgage payments by a safe margin. A common benchmark is 1.25x DSCR, but requirements vary. If your rental income is borderline, you may still obtain finance, but the lender might require a lower LTV, additional security, or a different structure.

Covenant Strength

For tenanted property, the tenant covenant matters. Stronger covenants generally support better lending outcomes, particularly if the lease is long, the rent is sustainable, and the property is easy to re-let.

Lease terms and property fundamentals

The unexpired term, break clauses, repairing obligations, and overall marketability influence lender appetite. A property with a weak or short lease may still be financeable, but lenders can become conservative if they see re-letting risk within the loan term.

Why rates and fees matter (and why the headline rate isn’t everything)

Commercial mortgages often include arrangement fees, legal fees, valuation fees, broker fees and sometimes exit fees. In some cases, lender fees can be added to the loan rather than paid upfront, which improves cashflow but increases interest cost. The calculator lets you model both approaches.

Rates can also be structured as two-stage products – for example a fixed period followed by a variable rate. In real lending scenarios, the payment often changes when the rate changes, so it’s worth stress-testing your affordability at a higher rate, not just the initial deal.

How to use the calculator properly

• Enter your purchase price and set the loan by LTV, deposit, or loan amount.

• Choose repayment or interest-only.

• Enter a realistic term (commercial terms are often shorter than residential).

• Input your interest rate – and consider testing a higher rate to stress-test.

• Add fees if you expect them, and decide whether they are paid upfront or added to the loan.

• If relevant, include a modest overpayment to see how it affects interest cost.

The results give you an indicative periodic payment, total interest over the term, and the end balance (particularly relevant for interest-only structures).

About this commercial mortgage calculator

This commercial mortgage calculator is designed to provide a high-level, indicative estimate of loan repayments and related metrics based on the assumptions you input. It allows you to model common commercial lending structures – including capital and interest repayment, interest-only loans, fixed rates and two-stage rate scenarios – so you can quickly assess whether a proposed purchase or refinance is broadly affordable.

The calculator works by applying standard amortisation principles to your inputs, together with simple assumptions around payment frequency and term length. Where a two-stage interest rate is selected, the calculator assumes that repayments are recalculated when the second rate period begins, based on the outstanding balance and remaining term. This reflects typical commercial lending practice but does not attempt to replicate the exact mechanics of any specific lender.

Importantly, the calculator does not assess lender appetite or credit policy. It does not take into account covenant strength, tenant risk, lease terms, property condition, marketability, valuation assumptions, debt service coverage ratios (DSCR), personal guarantees, or wider security arrangements. In practice, these factors are often decisive in whether finance is offered and on what terms.

Disclaimer

Before proceeding with a commercial mortgage, you should seek advice from an appropriately qualified mortgage broker, lender, solicitor and professional adviser, and ensure that all assumptions are verified against the specific property, borrower profile and loan documentation.

This calculator does not constitute financial, lending, legal or tax advice, and no liability is accepted for any reliance placed on its outputs. You should not make investment, borrowing or commercial decisions based solely on the results shown.