Developments after 1NT opening

Responses by bidding sequence

After 1NT opening, the responses are as follows:

Bid	Meaning	Developments
2C	Stayman (8+)	See here
2D	Transfer to H (5+ hearts)	See here
2H	Transfer to S (5+ spades)	See here
2S	Minor Stayman (9+, usu. unbal. and at least 5-4 in minors)	See here
2NT	Transfer to C (6+ clubs)	See here
3C	Transfer to D (6+ diamonds)	See here
3D	Looking for transfer to H (15+, exactly 5 hearts)	See here
3H	Looking for transfer to S (15+, exactly 5 spades)	See here
3NT	To play (10-14 balanced)
4C	Gerber (15+ balanced)
4D	Transfer to H (10+, 6+ hearts)
4H	Transfer to S (10+, 6+ spades)

Responses by responder strength

After 1NT opening, the responses according to responder strength are as follows:

Shape	Point range
	0-7	8-9	10-14	15+
Balanced	Pass	Bid 2C (Stayman) then 2NT	Bid 3NT	Bid 4C (Gerber)
4-card major(s)	Pass	Bid 2C (Stayman) then 2NT/3M depending on major fit	Bid 2C (Stayman) then 3NT/4M depending on major fit	Bid 2C (Stayman) to look for major fit and then explore slam
5-card major	Bid 2D/2H to transfer	Bid 2D/2H to transfer and then 2NT	Bid 2D/2H to transfer and then 3NT	Bid 3D/3H to look for transfer
6-card major	Bid 2D/2H to transfer	Bid 2D/2H to transfer	Bid 4D/4H to transfer	Bid 2D/2H to  transfer and then explore slam
5-4 in majors	Transfer to the 5-card major	Bid 2C (Stayman) and then 2M (the 5-card major) if opener denies 4-card major	Bid 2C (Stayman) and then 3M (the 5-card major) if opener denies 4-card major	Bid 2C (Stayman) and then 3M (the 5-card major) if opener denies 4-card major
5-5 in majors	Transfer to the better major	Bid 2D to transfer to hearts and then bid 2S	Bid 2H to transfer to spades and then bid 3H	Bid 2H to transfer to spades and then bid 3H
5-4 or better in minors	Pass	If unbalanced, either downgrade to 0-7 or upgrade to 10-14	Bid 2S and then show shortness	Bid 2S and then show shortness
6-card minor	Bid 2NT/3C to transfer	Either downgrade to 0-7 or upgrade to 10-14	Bid 3NT if balanced, or bid 2NT/3C to transfer and then show shortness	Bid 4C (Gerber) if balanced, or bid 2NT/3C to transfer and then show shortness

Remarks

1. It is also possible to bid 4NT/5NT (invite to 6NT/7NT) or 6NT/7NT (to play) over 1NT, but this is not encouraged.
2. If the 1NT opening is overcalled, the I-DO system applies if responder's bid is at or below (2S), and the DORA rule applies if opponent (doubles). Otherwise system is OFF and all subsequent bids are natural.