Two points, not two planets
The Moon's orbit is tilted by roughly five degrees against the plane in which the Earth goes round the Sun. Any two tilted circles intersect at two places, and those two places are the lunar nodes: the north node where the Moon crosses going upwards, the south node directly opposite. Eclipses happen when a new or full Moon falls near one of them, which is the whole reason the nodes were tracked in the first place.
The nodes are pulled slowly backwards by the Sun, so unlike the planets they normally move in reverse through the signs. A full circuit takes about eighteen years and seven months, which puts the first nodal return a little before nineteen and the ones after it near thirty seven, fifty six and seventy four.
Why the age is a range
The eighteen and a half year figure is an average of a wobbling motion rather than a fixed clock. The nodes do not glide evenly: their real motion speeds up and slows down over a period of about a month, and they can even edge forwards for short stretches, which is why some charts use a smoothed mean node and others the true node.
Between those effects the first return lands anywhere across roughly eighteen and a half to nineteen years, and later returns spread a little wider. The calculator above works from the node's position rather than adding an average to your birth date, so the answer it gives is your own.
There is also a half return at roughly nine and a quarter years, when the nodes have travelled half the circle and the north node sits where the south node began. Some astrologers count that reversal as part of the same cycle.
Repeat crossings near the return
Because the true node's motion is uneven, it can pass a degree, edge back over it and pass it again within a few weeks or a couple of months. That gives a short cluster of crossings rather than the long triple pass produced by a retrograde outer planet, but the principle is the same.
The tradition reads the whole cluster as one period rather than picking a date out of it. The widget above prints every crossing it finds, so a return with several passes shows up as several passes rather than a single line.
What the tradition makes of it
The nodes are conventionally read as an axis of direction, with the north node standing for what a chart is described as moving towards and the south node for what it already knows how to do. A nodal return is therefore read as the same axis coming round again, and the return near nineteen in particular is tied in the tradition to the point where a person starts choosing a direction rather than inheriting one. The difficulty it is associated with is the pull of the familiar, since the south node is read as the easier option and the one that quietly reasserts itself. All of that is interpretation, plainly marked as such, and it forecasts nothing about your life.
The houses holding your natal nodes are what make the reading specific, and those need a birth time. The dates themselves do not, because the nodes move only a few minutes of arc in a day.
Because eclipses cluster near the nodes, a nodal return often coincides with an eclipse season touching the same degrees, which is why older texts discuss the two together.
Questions people ask about this
When is my nodal return?
A little before your nineteenth birthday, then near thirty seven, fifty six and seventy four. The exact dates depend on your own node position, which the calculator above works out.
How long is the nodal cycle?
About eighteen years and seven months for a full backwards lap of the zodiac. That is the same period that governs the eclipse cycle, since eclipses occur near the nodes.
What is the difference between the mean node and the true node?
The true node follows the actual wobbling motion of the crossing point, while the mean node is a smoothed average of it. They can differ by a degree or so, which occasionally shifts a return date.
Are the nodes real objects?
No. They are the two intersections between the Moon's orbital plane and the Earth's, so they are geometry rather than bodies. That does not affect the calculation, which uses standard ephemeris positions.
Do I need a birth time?
Not for the dates, since the nodes barely move in a day. You need one for the houses, and the houses are what make an interpretation specific to your chart.
Does a nodal return mean a change of direction?
That is how the tradition describes it, and it is offered here as convention rather than as a finding. The checkable parts are the dates, the crossings and the houses the nodes occupy.