Cheapest flight from SIN to JFK
 

Or multi stop with sin, LHR, JFK, SIN

Any assistance would be appreciated.

Dirt Joe Welcome to FT

FT is not a travel agent or has a source of cheap fares
Try on line travel agents, kayak, google flights etc

The flight date is important to cost (you do not mention date)

Also search for RTW fares....as thats what you seem to be possibly doing...

Recommend giving matrix.itasoftware.com a look...

Using 8 to 22 March a simple return SIN-JFK (fr'instance) is as low as $798 on CZ (China Southern)

SIN-JFK (stop)-LHR(stop)-SIN around the same time as low as $1500 (but goes via LHR on the way to JFK so you might do better going to LHR first???)

Have fun...good luck,

LOL....just realised LHR first was likely the plan....:D

If you don't insist on stopping at LHR, Norwegian Air has flights from Thailand(short flight from SIN) to Oslo DY7202, which then has DY7001 to take you to JFK. Total for one way is about $515, worth considering.

Hope it helps!