SQL Server 2019

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create table offers
(
    ID int,
    FromDate date,
    ToDate date
);
insert into offers values
(1, '2022-01-02', '9999-12-31'),
(1, '2022-01-02', '2022-02-10'),
(2, '2022-01-05', '2022-02-15'),
(3, '2022-01-02', '9999-12-31'),
(3, '2022-01-15', '2022-02-15'),
(3, '2022-02-03', '2022-02-25'),
(4, '2022-01-16', '2022-02-05'),
(5, '2022-01-17', '2022-02-13'),
(5, '2022-02-05', '2022-02-13');
9 rows affected

with 
dates as
(
    -- get all date points
    select ID, theDate = FromDate from offers
    union   -- union to exclude any duplicate
    select ID, theDate = ToDate from offers
),
cte as
(
    select ID         = d.ID, 
           Date_Start = d.theDate, 
           Date_End   = LEAD(d.theDate) OVER (PARTITION BY ID ORDER BY theDate), 
           TheCount   = c.cnt
    from   dates d
           cross apply
           (
                select cnt         = count(*)
                from   offers x
                where  x.ID        = d.ID
                and    x.FromDate <= d.theDate
                and    x.ToDate   >  d.theDate
           ) c
)
select ID, TheCount, days = sum(datediff(day, Date_Start, Date_End))
from   cte
where  Date_End is not null
group by ID, TheCount
order by ID, TheCount


ID
TheCount
days


1
1
2913863

1
2
39

2
1
41

3
1
2913861

3
2
29

3
3
12

4
1
20

5
1
19

5
2
8