In regular contributions ... monthly, quarterly, half yearly and annually ... or lump sums.

Regular Contributions

The minimum contribution is:

$100 monthly
$250 quarterly
$500 half yearly
$1,000 annually

Changing Payments

You can increase your contributions, but when you do it has to be at least by:

$25 increase if paying monthly
$75 increase if paying quarterly
$150 increase if paying half yearly
$300 increase if paying annually.

Automatic Annual Increase

When you select this option, you may choose the percentage by which your regular contributions will be increased each year. The minimum is 3.0%.

Lump Sums

Payments as part of a regular contributions or lump sum plan:

$500 minimum.

Single payments, not part of any plan:

$2,000 minimum.