Budgeting is one of the main planning tools in any organisation. It involves estimating the time, amount and cost of resources required to achieve a specific objective. In the private sector the budget may be adjusted regularly during the financial year depending on income from sales. In the public sector, income is much less variable during the year as taxes and grants tend to be fixed annually in advance. Income from fees and charges is a much smaller proportion of income (albeit growing in many countries), and even here it is common for tariff levels not to be varied during a financial year.