Unbalanced Inheritance Division

Another possibility is that your sister is not as wealthy as you think she is.

Some people do a good impression of wealth while they are up to their eyeballs in debt. It's not beyond the possibility that she told your parents about this and they agreed to change the split.

The split itself seems "calculated". If she had been the favourite why not leave everything to her ?

Did your parents tell you about this before they died ? When was the will last revised ? Was there a difference for example between one parents will and the other ?

Do you have an Aunt or godparent that will leave you their money and it is an attempt to even things up ?

If you genuinely don't know the reason why this happened there are plenty of opportunities for investigation to try to discover why.

So what if she did? Circumstances differ. Just divide it equally

Always, always split equally, unless the other family member (s) is, a murderer, paedophile, imprisoned for a heinous crime, or locked away for life in a psychiatric unit or something equally serious.
No matter if parents fell out with a child, or one child provided more care, or was the favoured child, the poorer or richer child. To do anything else is vindictive and cruel and results in legal wrangling for years. I’m surprised the poll results aren’t be in 100% in favour of OP

It is extremely unfair, but there is a reason.

They may have wanted to compensate your sister for something you weren't aware of.
One of them may have made a promise or commitment to her during their lifetime?

One parent may have discovered later that they weren't the biological parent?

If it is as you say - not sure I could forgive my sibling for not doing a deed of variation.

you have to let this go. both of your parents have died, your sister isn't giving you any money.

accept it and move fwd. live your live now, as it is, you don't have another one

read some self help books maybe or so sort of therapy, professional or otherwise but you have to step forward.

you have 40k, more than most in the UK , and much much more than the vast majority of people in the world.

Aunts, uncles and other distant relatives are a different kettle of fish. If you have an aunt who prefers your sister to you for whatever reason, and that is reflected in her will, it doesn't cause you the existential pain of your parents preferring your sister to you. It's also much more natural for two siblings to have very different relationships with an aunt.

Your sister knows you are entitled to an equal share of the money. It was nasty of your parents to not share the money equally. I'd cut ties if my sister refused to share equally.

My childless aunt left twice as much to my sister because she helped her more than I did . She told me she was going to do it, and I said I understood. It was fair.

That’s terrible. How hurtful of your parents.

I think the unfairness would hurt me a lot so I could cut ties too.

There is usually is a backstory , particularity since the Op is reluctant to go into any great detail
My sil’s father died ( she is one of five ) .
She received fifty percent of the inheritance and the rest was shared among the four remaining siblings .
Her siblings were up in arms about this fact and made it clear that they thought it was unfair and told anyone who would listen
However, they didn’t mention the fact that my sil was the only person who took care of their father after their mother died . She attended all his hospital appointments , took him out to dinner and on family holidays .
Visited him over the Christmas period with her children . The other siblings didnt do anything to assist yet expected an equal share
Fortunately for them my sil shared the money equally because she didn’t want a rift in the family as she wanted to keep in touch with her nephews and nieces

You can only challenge a will if you are a spouse or in some way a dependent. Not true of healthy adult children with their own incomes.

Did she look after your parents more than you? Spend more time with them? Very odd otherwise

Yes that’s so very upsetting.
Similar happened to my Dad, he got 20% and his sisters shared the rest. They haven’t spoken since which has caused a huge rift and the family has been completely divided as a result.

I would be so hurt, and like you, if the shoe was on the other foot I’d immediately share with my sister. But is money worth losing your sister for?

Life is so short, don’t make any knee jerk decisions that you may come to regret.
Really hope it works out for you @Stilson x

It's not about anyone being 'forced' to hand money over, it's more that if someone behaves in a way that is unfair and selfish, it opens your eyes to the fact that they value money more than principle. You naturally struggle to respect and spend time with a person like that. Unfortunately people can always tell themselves a story about why they need more money than others even if to an outside observer it seems ridiculous.

ETA. You can do a deed of variation so there are no tax implications.

Yout anger is misplaced. Don't be angry with your sister be angry eith your parents. They created this situation.

Your dad didn't want the split to be equal and I don't blame your sister for accepting his choice. There must be more bad feeling between you for you to cut her off like this.

of course it means she's the favourite, what else do you think it means?

Not only she's the favourite, but they are making a massive statement about it, which is even weirder.

I know they are gone, and I am sorry for the OP, but that's awful behaviour. And I speak as a parent.

It's really not your sisters fault - unless you think it is and haven't mentioned.

It's also not as easy as her "correcting" your parents decision. There would be inheritance tax consequences for her own estate if she were to gift you the extra share you think she should receive (if she were to die in the next 7 years).

If this happened in my family I would be annoyed at my parents for putting me in an awkward position, but if I was forced to hand money over in order to maintain a relationship, I would also feel that the relationship was over anyway. So there's no win here for me.

If there is really no reason for the difference (no loans, extra support to OP previously that's being evened out now etc) and the sisters had a good relationship up to now it seems odd that the sister isn't willing to even things up.
However, in my experience the reality of actually having a large sum of money that you are legally (if not morally) entitled to can make people behave very selfishly.
For sexist, weird and historic reasons my siblings, cousins and I always knew that our rather odd grandmother planned to leave everything to the male grandchildren only. Each male grandchild had at least one sister and for as long as we'd been aware of this the boys had all agreed that it was not on and they'd all split their share with their sister/s. There were even discussions after they died about how this should be done (eg. split the total between all GC or split between the boys then they share with sister/s). It turned out that gran, who had lived a fairly dull and frugal life) had more money than expected so the boys were each due a sizeable sum. Suddenly everything changed. One cousin still shared with his sister but the others all found 'reasons' why they needed it more and gave their sisters a token amount (that we were all supposed to be very grateful for). Personally, it was a stepping stone in me seeing my brothers for what they were and not really wanting a relationship with them.

It’s a horrible feeling when this happens. I went through it my sister got everything. It was devastating. I had to have a lot of therapy to get over it.

We were NC and then 6 years afterwards her dh contacted me as they wanted me to agree to testing as she was in kidney failure and they expected me to step up and be tested !!!!

The will is not saying she's the favourite, it's saying she inherits more but the reason why is unknown.

i put UABU but only because you can’t make her. I think this is unfair, but you can’t force your sister to change it

Did you actually see the will ?

To me the probability that there was some funny business going one is far higher than the probability that an uneven split was given with no one having the slightest idea of why.

As other people have said, maybe there was some arrangement between your sister and parents, for example she gave them money to enable them to stay in their house if they didn't have enough. But unless she is willing to explain why (not quite sure why she wouldn't) you wouldn't know.

Have you asked your sister why the split is the way it is ?