6 Gross rental income and service charge income
| | 2015 | 2014 |
Theoretical rent | 167,986 | 163,179 |
Incentives | (1,378) | (1,431) |
Vacancies | (3,994) | (5,699) |
Total gross rental income | 162,614 | 156,049 |
The Fund leases its property investments in the form of non-cancellable operating leases. The nature of the theoretical rent has an indefinite duration because there are no fixed contract periods.
Service charge income represents € 4.0 million (2014: € 4.0 million) income receivable from tenants for the services of utilities, caretakers, etc. when the Fund acts as principal.