As mentioned, calculating SDLT on a commercial lease is complex, and while it is possible to use an online calculator, the calculators do not allow for all the complexities that may arise and so it is advisable to consult a tax lawyer or accountant who is well versed in handling commercial SDLT.nnThe SDLT rate is based on any lease premium paid by the tenant and on the rent due under the terms of the lease (including VAT if applicable).nnThe amount of ‘rent due’ is based on the first 5 years of rent payments. If the lease is longer than 5 years, the ‘rent due’ is based on the highest amount paid over a 12-month period during the first 5 years.nnOnce the length of the lease is factored in, the Net Present Value (NPV) of the lease can be calculated, and the amount of SDLT owed is based on this figure.nnSDLT can also be applied to certain other payments made under the terms of a lease, and also to ‘chargeable considerations’, such as a commercial tenant’s obligations to carry out work or services on a rented property.