Lump sum to provide a regular income

Good afternoon and I wanted to know how I can calculate how many years a certain sum will last bearing in mind a small pension I receive, but which needs to be topped up everyone month from our economies/certain sum? If there was a link to a site/Excel example, I could probably work on that. Many thanks in advance and have a nice day, Murdo

Hi Murdo: Try the Yahoo personal finance calculator by searching "How long will my money last with systematic withdrawals?" It is clear and easy to use.